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HOOKER'S 



NEW PHYSIOLOGY, 



DESIGNED AS 



A TEXT-BOOK 



INSTITUTIONS OF LEARNING. 



BY 

WOKTHIXGTOX HOOKER, M.D., 

PROFESSOR OF THE THEORY AND PRACTICE OF MEDICINE IN TALE COLLEGE. 
AUTHOR OF ** PHYSICIAN AND PATIENT.'" 

REVISED BY 

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1-74. 



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Electrotyped by Smith & McDotjgal, 82 Beekman St., N. Y. 



CONTENTS. 



CHAPTER I. 

PAGE 

Organized and Unorganized Substances 1 



CHAPTER II. 
The Distinction between Animals and Plants .. . „ . 9 



CHAPTER III. 

Man in his Relations to the Three Kingdoms of 

Nature 13 



CHAPTER IV. 
The Bones 17 

CHAPTER V. 
The Mt> i is 50 

OHAPTBB VI. 
The Lahi m the Musclbi 74 



IV CONTENTS. 



CHAPTER VII. 

PAGE 

Digestion 81 



CHAPTER VIII. 
Circulation of the Blood 105 

CHAPTER IX. 
Respiration 127 

CHAPTER X. 
Formation and Repair 155 

CHAPTER XI. 
Cell-Life 165 

CHAPTER XII. 
The Nervous System 178 

CHAPTER XIII. 
The Voice 205 

CHAPTER XIV. 
The Ear 219 



COXTESTTS. v 



CHAPTER XV. 

PAGE 

The Eye 228 



CHAPTER XVI. 
Hygiene 249 



PART II. 

CHAPTER XVII. 
Connection of the Mind with the Body 274 

CHAPTER XVIII. 

Differences between Man and the Inferior Animals... 292 

CHAPTER XIX. 

Var.eties of the Human Race 310 

CHAPTER XX. 

Life and Death 323 

33G 

Gloss lbt 866 

Index 374 



PREFACE. 



I, HAVE aimed so to write this book, that it shall be fitted both for 
general reading, and for instruction. It is designed for the family 
< 11 as for the school. It seemed desirable that these two objects 
should be accomplished at the same time, and I have not found them 
to be at all incompatible. The instruction needed by the family on 
this subject does not differ from that which is required in the school- 
room, either in regard to the facts to be commuuicated, or the manner 
in which it should be done. No one will question the truth of this, 
so far as the facts are concerned. But it is true even as to the mode 
of communicating them. In both cases there need to be clearness in 
statement, and fullness of illustration. Actual instruction is to be 
given in both cases, and to minds that are very nearly in the same 
attitude. I could not, therefore, see the necessity of writing a book on 
this subject for the people which should differ from one written for the 
school. Besides, it has seemed to me desirable that there should be a 
greater community of interest between the school and the family than 
as yet exists ; and this object, books equally interesting to both will 
tend to promote. 

I have avoided technical terms so far as possible. Whenever they 
are used they are sufficiently explained at the time, so that no glossary 
is needed. Some points commonly considered hard to be understood 
are treated of, but I have endeavored to simplify them, by full illustra- 
tion, and by a presentation of the truth uncomplicated with specula- 
tions and hypotheses. And these points are so introduced, that the 
mind is prepared by the previous investigation to understand them. 
I have aimed so to arrange the topics, as to have a preparation con- 
stantly going on in the mind of the student, fitting him for the proper 
understanding of what is to follow. By this natural gradation in the 
development of the whole subject some of the deep things in Physi- 
ology can be made clear, which it would otherwise be impossible for 
the student to understand. 

Although Physiology is becoming a prominent study in the schools 
and colleges in some parts of oar country, its importance is no where 
should be. It should be made a regular branch 
in our Educational System. This 1ms been already done in Prance. 
'A competent knowledge," reenter, "of Animal Physiology 

and Zoology is there required from every candidate for University 



Till PREFACE. 

honors ; and men of the highest scientific reputation do Dot think it 
beneath them to write elementary books, for the instruction of the 
beginner." 

The importance of Physiology as a study, will appear from various 
considerations. 

Many of the subjects comprised in Physiology have, in the case of 
most students, been already studied in a different phase, or mode, in 
other branches. Thus, if the student has attended to the Mechanical 
Powers in his Natural Philosophy, he finds in the human body the 
principles of the pulley and the lever illustrated in great variety and 
perfection. The principles in relation to strength in the form and ar- 
rangement of structure he sees exemplified in the framework of the 
body in the most admirable manner. If he has studied Hydraulics, he 
sees in the body the most perfect, and at the same time the most com- 
plicated hydraulic machinery, working incessantly throughout life in 
the circulation of the blood. The principles of Pneumatics he finds 
applied in the respiration — those of Optics in the eye — those of Acous- 
tics in the ear — and those of Musical Sounds in the apparatus of the 
voice. And then, his chemical knowledge meets with new applications 
in his observation of the changes and the processes going on in the body. 

The relations, then, of Physiology to some of the common branches 
taught in the higher classes in schools, are of the most intimate char- 
acter. Physiology, in part, merely extends these branches into a new 
and interesting field ; and the student who has once entered this field 
recurs to these same branches with a renewed interest. Hydraulics, 
Pneumatics, Optics, &c, have now a new attraction for him, from this, 
to him novel, application of their principles. The interest thus awak- 
ened in his mind is worth much in itself, aside from the mere addition 
made to his knowledge. And the interest is enhanced by the con- 
sideration, that in the human body he sees the applications of these 
principles to mechanism that exhibits the skill of perfect wisdom and 
almighty power. 

But there are relations of Physiology to still other studies which 
should be noticed. 

The analogies that exist between the human body and all other 
living things, in relation to structure and growth, are numerous and 
striking. Though life is so diverse in its processes and in the forms 
which we see it evolve in the whole range of animated nature, it in 
some important respects displays a great similarity, which it is interest- 
ing to trace throughout its diversified manifestations. Growth, or 
nutrition, as you will see in the following pages, is essentially the same 
in the Plant as it is in the Animal. Botany, therefore, taught as it 
should be, has quite an intimate relation to Animal Physiology. The 
Science of Life is, in many respects, one Science ; and if, in studying 
any of its subdivisions, we fail to take this broad view of it, and to trace 



PREFA< IX 

out the analogies referred to, we lose a large part of the interest of the 
study. Human Physiology, the subject of study in this book, is but a 
part of a science which otters to the student wide fields of observation 
exceedingly diversified and full of interest. This being so, I could not 
avoid in the following pages making occasional references to the analo- 
gies existing between the phenomena of life as exhibited in the human 

m. and those which we see in the living world around us ; and as 
the student proceeds with the study, he will tind himself interested in 
in whatever form they are presented. 
This leads me to say that this study of nature, in its broad common 
relations and its beautiful and extensive analogies, should be made very 
prominent in our systems of education. It is the application of the 
principles of abstract science to the forms, and especially the licit) g 
forms of nature all about us, that gives interest to these principles, and 
makes us to understand and appreciate them. It is here that we find 
a very serious defect in the prevalent mode of education, even at the 

Dt time, notwithstanding all our improvements. We live in the 
midst of a material world, animate and inanimate, and have daily con- 
to speak, with material forms of every variety, presenting phe- 
nomena of the highest interest and of endless diversity. And yet, 
through almost all the period of childhood, and perhaps we may say 
youth also, this book of nature is in the school-room very nearly a 
sealed book. The very process of education shuts in the pupil from 
this broad contemplation of the world in which he lives. He is drilled 
through spelling, reading, grammar, &c., but he is left in total ignor- 
ance of the beautiful flowers, and the majestic trees outside of the 

il-room. How very few even of thoroughly educated adults, know 
the processes by which a plant or a tree grows! And the same can be 
said of other phenomena of nature. 

The defect which I have pointed out runs through the whole of edu- 
cation. We can see it even in the prevalent mode of teaching the 
natural sciences themselves. One would suppose that here the facts, 
the phenomena, would command the chief attention of the teacher and 
student. Bur it is very commonly not so. The mere technicalities 
and the classification are made much too prominent. Botany, really one 
of the most interesting of all branches of natural science, is thus 
ordinarily made one of the driest of studies. To track this aright, tfie 
getation, s > varied and so beautiful, should constitute tlie 
. and the mere classification should be con- 
i /■//. as wholly a secondary tlnnrj. 

The great faets of the world, both of mind and matter, should 

furnish really the material for education and those branches that are 

ordinarily pnrsoed with such assiduity Bhould be considered as merely 

idiaryto the teaching of these facts. The whole order of education 

must be reversed. In.-tead of beginning the child's education with 



X PREFACE. 

learning to spell and read, the object should be to make him an ob- 
server of nature, and the spelling and reading should be done in con- 
nection with this, and as subsidiary to it. Things and not words, or 
mere signs, should from the first, constitute the substantial part of in- 
struction. The child should be made, at home, in the school, and every- 
where, a naturalist in the largest sense of that word. We should aim 
to impart to him a spirit in consonance with the following precept of 
Hugh Miller, the famous self-taught geologist : " Learn to make a 
right use of your eyes ; the commonest things are worth looking at — 
even stones and weeds, and the most familiar animals." 

As it is now, no one becomes a naturalist early in life, except in 
spite of the tendencies of his education. The study of nature is not 
only not encouraged, but is absolutely discouraged in our educational 
system. If any one, like Hugh Miller, by the force of a taste that can 
not be repressed by the training of the school-room, undertakes to 
make a " right use of his eyes," and curiously examines " stones and 
weeds," he is regarded by the world of spellers and readers and gramma- 
rians and cipherers, as a strange genius. But he is pursuing, from an 
irresistible internal force, the very course that I would have every 
student, even from his childhood, encouraged to pursue, in a measure 
at least, by the external circumstances of his education. The tenden- 
cies of his training should be decidedly in this direction. 

If the general mode of education were changed in the manner indi- 
cated, education would have much less of the character of mere drudg- 
ery than it now has. Not that there would be any the less labor ; but 
the labor would be made lighter by the interest imparted to it — the 
interest which always results from the study of facts and phenomena, 
and never from the learning of mere words and technicalities and 
classification. I would gladly dwell on this subject, and show by 
varied illustrations how the mode of instruction referred to, should be 
pursued, and especially with younger scholars ; but the limits of a 
preface will not allow me to enter so large a field. 

The change which I have pointed out can not be effected at once. 
It will require time. Confirmed traditional customs are to be done 
away, the habits of teachers are to be altered, and the projfer books are 
to a great extent to be yet written, especially such as are fitted for the 
first years of education. 

If the study of nature should be thus made prominent in education, 
human physiology would be considered altogether its most interesting 
and important branch, and for several reasons. First: there is no- 
where to be found so curious a collection of mechanisms, or so interest- 
ing and wonderful a series of processes, as in the human body. In 
nothing else in the wide world are the principles of so many depart- 
ments of science so extensively and perfectly exemplified. Life works 
here its most complicated set of machinery. Secondly : the singular 



PREFACE. XI 

and mysterious connection of the immaterial and immortal soul with 
the material and perishable body, gives intense interest to this study. 
In Physiology we do not study matter alone, or spirit alone, but both 
matter and spirit united, and often acting together. This circum- 
stance distinguishes this from all other studies. Thirdly : it is our own 
frames, moved by the spirit within us, that we study. The subject has 
a personal interest for us that is not presented by most studies, and 
by none In so large a degree as in this. And, fourthly : the study is 
of great importance, because a judicious and efficient Hygiene must 
be based upon a knowledge of the laws of physiology. We can 
not know how to keep our functions in the condition of health, with- 
out understanding the laws that regulate them. I have said but 
little in this book in regard to hygiene, and that only incidentally, 
because that subject would require of itself a whole volume to eluci- 
date it properly. 

I have not thought it proper to indulge to any great extent in those 
reflections which the contemplation of so perfect and diversified a 
l lies of mechanisms as are presented in man would naturally 
suggest, in regard to the skill of the great Builder of the universe. 
Such reflections would extend the book to too great length. Besides, 
they are so readily suggested to the mind of both teacher and scholar, 
that it is entirely unnecessary for the author to dwell on them. 

I have treated of some subjects on which, from the difficulty of 
understanding them, there has been a disposition in many minds to go 
beyond what we know, and indulge in unwarranted speculation. On 
these points I have taken pains to draw the line very distinctly be- 
tween what is known, and what is supposed. I deem it important to 
prevent the minds of the young from being led away from the simple 
truths of science by ingenious speculations and plausible reasonings. 
Let me not be understood to decry all hypothesis. I object only to the 
mingling of facts and suppositions together in one indiscriminate mass, 
a- is often done. The disposition to do this, which is more common 
than is generally supposed, exerts so injurious an influence upon the 
habits of the mind, and so confuses its views of truth, that we ought 
to look upon it as one of the most serious evils to be guarded against 
in education. It is really one of the most prominent obstacles to the 
pmirress of truth on all Bubjects, both in individual minds, and in the 
minds of tie- community at large. This disposition, so apt to I 
I in the enthusiastic mind of youth, by ingenious but d* 

should be corrected at the outset, and the mind should, 
in its forming Stage, be habituated to the discrimination between the 

proved, the true, and that which rests on presumptive, perhaps merely 
plausible This discrimination should therefore be exempli- 

fied in books designed for instruction, and this I have attempted in the 
volume, 



SUGGESTIONS TO TEACHERS. 



In order to be able to teach from this book properly, the teacher 
should himself study all of it thoroughly before he begins his instruc- 
tion. If he merely keep a little in advance of his class, he will fail in 
his conceptions of the general scope and plan of the book. If the 
interest of the subject awaken in him and in his pupils a spirit of in- 
quiry, there will be a continual looking forward to points which are 
explained and illustrated further on in the book. 

Now if the teacher has made himself master of all the subjects 
treated of, instead of turning off the inquiry of a scholar without an 
answer, or even the promise of an answer in the future, or endeavor- 
ing to clear up the points about which inquiry is made, which of 
course he can do, under the circumstances, in an imperfect manner at 
the best, he can satisfy the scholar by informing him that these points 
will be found explained in their proper place at a future stage of the 
investigation. 

I have aimed to have every topic treated of in its right place in the 
development of the general subject, and the teacher should be thor- 
oughly master of the whole book at the outset, in order that he may 
fully carry out my plan in the mode of developing the topics to the 
minds of his pupils. 

It must be obvious to any teacher that he can teach the minutiae of 
the subject with more of interest, to say nothing of thoroughness, if, 
while doing it, he takes in the general views presented, and has in 
mind the relations of the particular topics in hand to other branches 
of the subject. Indeed it will be profitable occasionally for the 
teacher to afford the scholar some glimpses of the interesting fields to 
be explored further on, taking care, however, not to anticipate so 
much as to mar the natural method and order of developing the 
whole subject, which I have taken such especial care to observe in the 
preparation of the work. 

The teacher should read the book through in course. If, instead of 
doing this, he opens to some chapter in the middle or latter part of the 
book, he may get the impression that too high matters are treated of, 
and that the minds of his pupils are not competent to understand 
them. They cannot be understood unless there be a preparation of 
mind for them ; and just this preparation is aimed at in the first part 
of the book. And besides, it is quite important that the subjects 
treated of should be developed to the mind of the teacher in the 
same order in which they are to be developed to the minds of his pupils. 



SUGGESTIONS TO TEACHERS. Xl.l 

In the engravings, clearness has been aimed at rather than beauty. 
Yet I should not do the engraver justice if I did not say, that in beauty 
they are generally quite equal to those which we find in our standard 
professional works on physiology. It is to be borne in mind that 
woodcuts cannot represent correctly the beauty and delicacy of living 
structures. These can be realized only by seeing the structures them. 
selves. Another thing to be kept in mind is, that parts which are re- 
presented in engravings with definite lines for the sake of distinctness, 
are ordinarily not thus distinct in the structures. To make them so, 
the dissecting knife must separate them, and take off the cellular sub- 
stance, which, as the general packing material of the body, everywhere 
connects adjacent pans together. 

The teacher can be aided very much in giving his scholars a correct 
idea of different organs, by presenting to them organs taken from the 
bodies of animals. Thus, in giving them an idea of the lungs, the 
lungs of a calf or a sheep can be used. A pipe may be fastened into 
the windpipe ; and by blowing into this, you can show how the iungs 
are inflated. An idea of the appearance of the human brain can be 
given by means of the brain of a calf, or any other animal of suf- 
ficient size. An ox's heart may be used in showing the structure and 
arrangement of the valves and other parts of that organ, for they are 
essentially the same as in man. A very good idea of the arrangement 
of the cartilages that make up the larynx, can be obtained from the 
larynx of an ox or a cow. The general shape and arrangement are 
me as in man. 

It is some trouble to clear the parts of muscular substance, but the 
teacher can get some physician or medical student to do it for him. 
When the preparation is once made, it can be dried for permanent use. 
I have one which I made twenty-five years ago. In drying, it will be 
necessary to keep the wings of the thyroid cartilage apart by a wedge, 
and the supple epiglottis must be placed in such a position as not to 
interfere with a view of the interior of the larynx. The large eye of 
the ox can be made use of to show the various parts of that organ, 
and also to show the formation of the images of objects on the retina. 

One great advantage of thus using parts from different animals is, 
that a taste is given for the examination of the phenomena of life, 
with its wonderful mechanisms, wherever they may be seen. All 
living nature thus becomes full of suggestive interest to the young 
stud 

There are some things of which platos can give no correct idea. 
Such, for example, is the ct'llular membrane. The attempt to r 
sent it is made in most books on physiology, but it is an entire failure. 
I have a plate representing its cells as seen in a dried preparation 
under the microscope; but to give the Bcholaran idea of i 
pear> taked eve in its natural condition, 1 refer him t<> 

seen in any common piece of meat between the muscles and between 



XIV SUGGESTIONS TO TEACHERS. 

the fibres of each muscle. The teacher can use a piece of meat for 
this purpose. The difference between muscles, tendons, and ligaments 
can be shown in the same way. 

Those figures which are mere diagrams it will be well for the 
scholar to draw on the blackboard, and his skill in description and re- 
mark may be exercised for his own benefit and for that of the class. 
He should be trained in this exercise in such a way that he will ac- 
quire the power of giving well-proportioned and well -arranged de- 
scriptions, without the aid of prompting by minute questions from the 
teacher. 

It will be proper to say something of the use which should be made 
of the questions that I have prepared. I have two . reasons for not 
placing them at the foot of the page. One reason is, that the book 
is designed for general reading as well as for instruction. But the 
chief reason is, that I wish to prevent a too free use of questions on 
the part of both teacher and scholar. The marking with the pencil 
of parts which contain the answers to the questions, so often done in 
our schools, should never be permitted by the teacher, for reasons that 
I need not stop to notice. 

The scholar should read the text at first without reference to the 
questions ; and then the questions can be made use of, perhaps with 
profit, to fix definitely in the mind the principal points that are 
brought out. It will be a useful exercise for the scholar, after reading 
a page or two, to think over the main points, and then see by the aid 
of the questions whether any important point has escaped his recol- 
lection, or failed to make the proper impression on his mind. 

The questions that I have constructed will, I think, be found to be 
fitted to the great majority of scholars. But of course the teacher 
will vary them to suit the different capacities and mental attitudes 
which he finds in his class. 

It is best not to have an uniform mode of asking questions, even 
with the same scholar. Variety should be given to the mode of hear- 
ing the recitation. Sometimes the questions should be minute, and at 
other times the mind of the scholar should be left to go on with as 
little leading as possible. 

The scholar should be encouraged occasionally to give the substance 
of a whole paragraph, or even of more than this. In doing so, any 
failure in arrangement or proportion can be noticed by the teacher, 
for the benefit not only of the scholar that is reciting, but also of 
the whole class. The general scope of an argument may also be 
given in the same way, and the manner of doing it be made the sub- 
ject of criticism. 

The numbers attached to the questions refer to the pages, this being 
more convenient to the scholar than a numbering by paragraphs would 
be, though of course it cannot be quite so definite in all cases. 



Physiology and Hygiene. 



CHAPTER I. 

ORGANIZED AND UNORGANIZED SUBSTANCES, 

1. Tlie Crystal and the Plant are both wonderful 
groicths. The crystal was once a minute nucleus, and the 
plant was once a little germ. 

In one respect they are alike in their growth — both have 
increased from particles taken from things around them. 
But the processes by which this is done are different in the 
two cases. The crystal has increased or grown by layer 
after layer of particles. Any part of it, when once formed, 
is not altered. It can receive additions upon the outside 
alone. The plant enlarges by particles which are intro- 
duced into passages and interstices. It grows by absorption 
or by intussusception. 

2. Organs, — This absorption is effected by certain ves- 
sels or organs, constructed in the root of the plant for this 
purpose. These absorb or take up fluid matter from the 
earth. Other organs circulate this fluid through all the 
plant ; and still others use it for the purpose of growth or 
formation* There are no such organs in the crystal, for it 
has no inner growth. The plant is therefore said to be an 
organized substance or being, and the crystal an unorgan- 
ized substance. 

3* Mechanical Principles. — These organs, which 
thue absorb, and circulate, and construct, do not act simply 
on m al principles. They are active agents, and they 



2 PHYSIOLOGY AND HYGIENE. 

perform their duty with a force, and after a manner, for 
which no mechanical principles can account. No mechan- 
ical powers could alone supply the leaves of the mighty 
tree of the forest with sap from its deep roots ; much less 
could they form those leaves. 

4. Chemical Principles. — Neither do these organs 
act simply on chemical principles. While man, through the 
agency of chemistry, can form some of the crystals which 
are found in nature, he can not by any arrangement of 
constituents make a plant, a flower, or a leaf. And the 
plant, left alone to the action of chemical principles, wilts ; 
and at length ceases to be a plant, and becomes common 
unorganized matter. 

5. Vital Principles. — Mechanical and chemical 
principles, it is true, are both exhibited to .some extent in 
the growth of plants ; but they are under the control of 
other principles, which we term vital. So the plant is not 
only an organized substance, but a living being. 

6. Animals. — What has been said of plants, in dis- 
tinction from minerals, may also be said of animals. They 
are also organized living beings, and they have, generally, a 
more complex organization than plants. 

The whole material world, then, that we see around us, 
we divide into two parts — the unorganized and lifeless, and 
the organized and living. The distinctions thus pointed 
out between organized and unorganized matter are essential 
and fundamental. But let us look at some other distinc- 
tions, which either arise from these or accompany them. 

7. Other Distinctions between the Organic 
and Inorganic. — All the parts of the mineral are inde- 
pendent of each other, while it is otherwise with the plant 
or the animal. Accordingly, we do not examine the proper- 
ties of plants and animals as we examine those of minerals. 
The chemist can ascertain all the properties of a crystal 
or a rock if you give him but a small piece of it. 

But the botanist can not ascertain all the properties of a 
plant by looking at some one part of it. If he examine the 
flower, this gives him no knowledge of the root. In order 



ORGANIZED AXD UNORGANIZED SUBSTANCB& 3 

to know all about the plant, he must examine every part by 
itself, and then look at it in its relations to the other parts. 
The same may be said of the physiologist, in his investiga- 
tion of the properties of animals. 

S. Assimilation in Organized Substances. — 
As the crystal is forming by layer after layer of particles, no 
change is effected in these particles as they are becoming 
arranged in the layers. But in the case of the living organ- 
ized being, a change is produced in the particles which are 
taken up by the absorbents. And the change, ordinarily, is 
both a gradual and a complex one. In the plant, a change 
is produced in the particles in the very act of absorption ; 
but this change is only the beginning of a process which is 
afterwards perfected. The sap is not thoroughly fitted for 
nutrition when it first begins tp circulate. It is carried up 
through the vessels of the trunk or stalk to the leaves. 
There the last step of the process is taken, and the sap is 
now ready to be used in the growth of the plant or tree. 

So, also, in the animal, the nutritious part of the food, 
taken up by the absorbents in the digestive organs, is first 
acted upon by certain little glands, through which it passes, 
is then poured into the circulation, to be mingled with the 
blood, and is carried with the blood to the lungs, to be ex- 
posed to the air ; and thus it is fitted for the nutrition or 
growth of the body 

This process, which is thus carried on in the plant and in 
the animal, is very properly called assimilation. For the 
particles that are taken up by the absorbents in the root of 
the plant are, by this process, made like to the plant ; and 
the particles taken up by the absorbents in the stomach* 

* The word stomach requires some little explanation, as it is used in 

physioloiry in two senses — in a limited sense, and also in an extended 

It is U3ed in its limited sense, as referring to the cavity at the 

j of the alimentary eanal, as it is termed; this latter term 

beinf: Applied to the series of cavities, the stomach and the small and 

irhich are found in the digestive apparatus in the 

of animals. In comparisons, however, between fcl 
animals and those whirh have a more simple digestive apparatus! the 
word stomaeh is \ised in a more extended ! ttonymom 



4 PHYSIOLOGY AND HYGIENE. 

are made like the animal. So obvious is this, in the case of 
the animal, that some French physiologist speaks of the 
blood as chair coulante, or running flesh. 

9. Permanency. — Another prominent distinction be- 
tween organized and unorganized substances is in relation 
to permanency. Constant change appears in all organized 
bodies; while permanency is written upon all substances 
which are unorganized. In organized beings, continual 
change is going on at every point. It is a condition of their 
being. 

This is true, not only of the decline of a plant or animal, 
but even of its growth. For, in its growth, as the parts en- 
large internally as well as externally, they change not only 
the arrangement of the particles, but, to a great extent, they 
change the particles themselves. It is true, as well of the 
towering tree as of the tiny plant, that these changes have 
been going on during all its growth ; so that, at its ma- 
turity, it is, both in relation to the arrangement of its par- 
ticles and in relation to the particles themselves, a very 
different thing from what it was when it pushed its germ 
up through the ground, or even when it was but a small 
tree. So, in all animals, the same internal changes are 
going on, and to a much greater extent ; because, from the 
activity of their nature, there is wear and tear, and, there- 
fore, refuse matter to be disposed of. As you will see in 
another part of this book, the human body undergoes these 
changes very largely. 

The crystal, as fast as it is formed, becomes permanent. 
No changes occur within it. In itself, it is unchangeable. 
It can not change its own particles, as the plant or the 
animal does. It can be changed only by external addition, 
or by external diminution, through the influence of agents 
acting upon its surface. 

10. Hepvo&uction. — With the constant changes 
going on in organic nature, there is constant succession. 

with the term alimentary canal. It is used in this sense, also, when, 
as in the present case, it is referred to in a comparison between animals 
and vegetables. 



ORGANIZED ANI> UNORGANIZED SUBSTANCES. 5 

Plants and animals produce other plantfi and animals, and 
themselves die, making room for their successors. But the 
crystal does not form other crystals, and then crumble into 

3t In itself, it is both unchangeable and unproductive. 

11. Observations of Change and Perma- 
nency* — This distinction between organized and unor- 
ganized substances, in relation to change and succession, 
meets the eye everywhere. The mountains, the rocks, and 
even the stones under our feet, remain the same year after 
year, while all vegetable and animal life is ever changing 
its forms and manifestations. There are the changes of 
growth, and the changes of decay and death, all around and 
within us : and they are strangely mingled together. 

There is death even in the changes of life, as the waste 
particles are taken away, and are replaced by the new r ; and 
life springs out of the very bosom of death, as from decayed 
nature new forms of vigor and beauty arise. The moun- 
tains stand as they have stood, as the passing generations 
have looked upon them, while the continual changes of 
vegetation have been going on upon and around them. 
The seasons crown their battlements with the emblems of 
their ever-returning mutations of life, decay, and death, 
and even the mighty trees, that have shed their leaves from 
year to year, in obedience to the great law r of change, but 
have themselves stood, at length bow their heads to the 
same law, and give place to other lords of the forest. 

From the "everlasting hills," which thus remain the 
same, though change is ever about and upon them, man gets 
the unchangeable and imperishable rock to construct his 
habitation, while he himself is changeable and perishable — 
the creature of a day, whose life is as a vapor. He wears 
the precious . and traffics in the golden ores, which 

have from the creation of the world, through all the 

iging and dying generations, and passes away, leaving 
them to other- as changeable and perishable as himself 

/?. forms. — Another distinction between organized 
and unorganized sul to the forms which they 

assume There is regularity in both, but it is different in 



6 PHYSIOLOGY AND HYGIENE. 

each. Unorganized matter is disposed to arrange its parti- 
cles in straight lines, and with angles mathematically exact. 

The tendency is to regularity ; and irregularity is the 
result of interfering circumstances. A similar disposition 
to regularity is manifest in organized substances, but in a 
different manner. They are disposed to curved, rather than 
straight lines, and seldom make lines or angles with mathe- 
matical exactness. We see this law of regularity exempli- 
fied both in animal and vegetable life. The leaf, for exam- 
ple, has the same general shape, that is, the same general 
arrangement of particles, when it attains its full size, that 
it had when it was small ; and the same can be said of the 
arm of the man, compared with his arm when a child. 

13* Regularity. — This regularity is more wonderful 
in organized substances than in the unorganized, because 
it rules in them in the midst of constant change. In the 
case of the crystal, as there are no internal changes in it, 
and as each layer of it, when formed, is permanent, regu- 
larity is comparatively, so to speak, easily secured. But in 
the case of the leaf, as it is growing to its full size, and of 
the arm, as it grows from infancy to be the stalwart arm of 
manhood, continual change is going on at every point ; and 
regularity here is obviously a more difficult achievement. 

This regularity appears still more wonderful, when we 
look at the infinite variety of forms in organized matter, in 
both the vegetable and the animal world. In all these forms, 
each part of every animal and of every plant maintains its 
own peculiar plan and contour. Take, for example, the leaf 
in its endless varieties. How definitely does each variety 
preserve its individual character, and how easily is it dis- 
tinguished from every other variety ! The same can be said 
of every part of every organized being. 

14. Persistency of Form. — Another circumstance 
still must be mentioned, as adding to the wonderfulness of 
this regularity. It has been scrupulously maintained, 
through all the changes of the world from its creation, 
when God pronounced the works of his hands to be "very 
good." The leaf of every tree, for example, is like the leaf 



ORGANIZED AXD UNORGANIZED SUBSTANCES. 

of its ancestral trees back to that time ; and so it will be in 
all its successors to the end of the world. - The trees of the 
garden," which delighted the eyes of our first parents, and 
refreshed them with their shade in their innocence, and 
amid which alter their sin they hid themselves from the 
presence of their Maker, undoubtedly had the same charac- 
teristic shapes, and the same leaves and flowers which their 
successors present to our eyes. 

15. Variety of Fo)*m. — Again, it is interesting to 
notice that, in the midst of this regularity, so strictly main- 
tained in each specific form from age to age, there is a 

bsure of irregularity allowed. While each kind of tree, 
example, has specific characteristics in the arrangements 
ranches and other parts, and in the shapes of its leaves, 
n<» two trees of the same kind are exactly alike, and there is 
always much variety in the leaves of the same kind. AVhilc 
the face of man is so entirely different from the face of 
every other animal, at the same time, among the hundreds 
of millions of the human family, how uncommon it is to 
find two faces that are very nearly alike. 

16. Sym metiry of Halves. — In the animal world, we 
Bee remarkable examples of the preservation of regularity of 
form in the exact correspondence which exists so commonly 
I'tt ween the two halves of the body. 

The brain has two halves, which are precisely alike, and 
the same is true of the nerves Avhich are distributed from it. 
And bo of other parts. But, mingled with this symmetri- 
cal arrangement of parts, there are other parts which are ir- 
regular in their shape. This is the case with the stomach, 
heart, the liver, &c. There arc some animals which 
altogether destitute of this arrangement of two similar 
halves of the body. The oyster La a familiar example. The 
I i i this animal is strikingly in contrast, in this respect, 
with the shells of Borne other of the bivalve tribe, as, for 
common clam 
11. Size.—T b distinction between organized and 

unorganized Bubstances, in regard to size. The size of un- 
sized bodies has no fixed limit A crystal or a rook 



8 PHYSIOLOGY AND HYGIENE. 

may grow to any imaginable size, if the particles forming it 
are sufficiently abundant. But organized bodies have limits 
fixed to their growth. There is, it is true, more or less lati- 
tude to these limits ; but they are so well defined in the case 
of most vegetables and animals, that when growth reaches 
much beyond or below the limit, it is recognized as a re- 
markable fact. 

18. Structure and Elements. — The last distinc- 
tion, between organized and unorganized substances, which 
will be mentioned, relates to their structure. While unor- 
ganized substances are made of one form of matter, either 
solid or liquid, or gaseous, organized bodies are made of a 
mixture of fluids and solids. They are therefore more or 
less soft and flexible ; while the solid, unorganized sub- 
stances are hard and brittle. 

There is a still further difference in structure. Organized 
substances are much more compound than the unorganized. 
Most of the unorganized substances are composed of only 
two or three elements. Thus, air is composed of oxygen and 
nitrogen, water of oxygen and hydrogen ; and most of the 
mineral salts are composed of three elements — as, for ex- 
ample, carbonate of lime, or chalk, which is composed of 
oxygen, carbon, and calcium, the mineral base of lime. 

But organized substances are composed of at least three or 
four elements and sometimes more. The four principal ele- 
ments in the composition of organized bodies are, oxygen, 
nitrogen, hydrogen, and carbon. But there are other ele- 
ments introduced for special purposes. Thus, carbonate of 
lime (a combination of calcium with two of the common 
elements, carbon and oxygen,) is diffused very generally 
throughout the textures of plants, giving them firmness 
and strength. In animals of the higher orders, phosphate 
and carbonate of lime compose in part the framework of 
the body. 

We find iron, too, in the blood. Of the sixty-four ele- 
mentary substances discovered in mineral bodies, only eigh- 
teen or nineteen have been found in plants and animals, 
and some of these in very small amounts. The essential 



THE DISTINCTIONS BETWEEN ANIMALS AND PLANTS. '.) 

components of living substances are the four non-metallic 
elements mentioned above — oxygen, hydrogen, nitrogen, 
and carbon : while the bulk of the inorganic world is com- 
posed of the metals and their compounds, viz., the alkalies and 
the earths. And it is interesting to observe that, of the 
four elements which compose the bulk of the animal and 
vegetable world, both the fluids and the solids, three are 
u<, while but one, carbon, is a solid substance. 



CHAPTER II. 

THE DISTINCTIONS BETWEEN ANIMALS AND PLANTS. 

HAVING pointed out the distinctions between organized 
and unorganized substances, w r e will now consider the dis- 
tinctions between the tw r o classes of organized beings — 
animals and vegetables ; first noticing those differences which 
are obvious; and second, pointing out those which arc 
tial 

UK Locomotion. — One of the most obvious distinc- 
tion- i- in relation to locomotion. The plant remains in one 
place: while the animal moves about, in the air, or in the 
water, or upon the surface of the earth. And the structures 
of the animal and the plant of course differ, so as to ac- 
commodate these two very different modes of existence. 

As the animal moves from place to place, it must, for 
this reason, if for no other, have an apparatus of nourish- 
ment and growth different from that of the plant. The 
plant, by means of its absorbents in the roots, takes up 
from the earth, in the form of sap, its nutrition, or food, as 
it may very properly be called. The moving about of the 
animal would in itself forbid its deriving Its food directly 
from the earth, even if the earth contained the proper 
materials for it- nourishment. 



10 PHYSIOLOGY AND HYGIENE. 

So a cavity is provided in its body, called a stomach, 
into which nutritious substances can be introduced. And 
this cavity is lined with absorbents, which there do for the 
animal what the absorbents in the roots of the plant do for 
the plant. 

20. Central Organs. — Besides the stomach, there 
are other great central organs which are peculiar to most 
animals, in distinction from vegetables — as the heart, the 
liver, the lungs, etc. Branches and roots may be cut off 
extensively, and even a large portion of the stem or trunk 
may be destroyed ; and yet what remains of the plant may 
still live. Even a small portion of it may be made to take 
root and live by itself. It is not so with most animals. 
Mutilation can not be carried far without injuring some 
large organ which is essential to the life of the whole ; and 
no part taken from its extremities can be made in any way 
to live by itself. 

21. Sensation and Voluntary Motion. — Another 
obvious distinction is this : The higher order of animals 
are sentient and spontaneously-moving beings, while vegeta- 
bles are not. The animal feels the action of agents upon 
it, and this it can not do without consciousness and thought. 
The evidences of the existence of consciousness and thought, 
and the consequent spontaneous motion, are very slight 
in some animals. We see these evidences plainly in the 
great majority of animals ; and we infer the existence of 
sensation and thought in those exceptional cases, where the 
evidences are doubtful or absent, as we find in them other 
marks of animal, in distinction from vegetable life. 

22. Exceptions.— The distinction in regard to locomo- 
tion, if we look at the animal as a whole, has its exceptions. 
There are some animals, as the coral animal and the sponge, 
that are entirely confined to one spot during all their ex- 
istence. But, while some animals are thus confined, they 
have the power of spontaneous motion in some of their 
parts, which is exercised for the purpose of obtaining food, 
and, in some cases, for the avoidance of danger. 

This power is not possessed by any plant. Some few 



THE DISTINCTIONS BETWEEN ANIMALS AND PLANTS. 11 



Fig. 1 



plants, as the sensitive plant and the Venus's fly-trap, 
(Dionaaa museipula.) exhibit a property which resembles it, 
but it is essentially a different thing. In these cases, the 
influence of the stimulus that excites the motion is com- 
municated from particle to particle, from the point where 
the stimulus is applied ; and the motion is only in one 
direction, and not in various directions, as is the case with 
spontaneous animal motions. 

23. Illustration. — This can be very readily seen, if 
we compare the motion of the sensitive plant or the fly- 
trap with those of the little fresh-water polyp called the 
Hydra, This animal, of which an enlarged representation 
is here given, and also a representation of its natural size, 
is found in ponds. It attaches itself to any floating object 
— a stick or straw, as seen in the Figure — by a kind of 
sucker. Thus supporting itself, it stretches out its long 
arms, to take for its food any 
minute worm or insect which 
may float within their reach. 
When it catches one, it directs 
the mouth, a. which opens 
into the stomach or general 
cavity. Xow, in doing all this, 
there is a variety, a compound 
character in the motion, which 
is in plain contrast with the 
simple motion of the leaves of 
the fly-trap and those of the 
:tive plant. 

^4. Nervous System. — 
ttdingly, we find a peculiar 
Ftriu-turc in animals devoted to 
functions, and others con- 
• I witli them. This struc- 
ture u the nervous system. No trace of such a structure 
has ever been discovered in any plant If there were any 
true analogy between animal motion and the motions of the 
itive plant and the By-trap, we should be able to find in 




HYDIU. 



12 PHYSIOLOGY AND HYGIENE. 

them traces of nervous structure; for the structure of 
these plants is so plainly developed, that its constituent 
parts are easily distinguished. It is true, also, that in some 
of the lower animals no trace of a nervous system is found. 

25. Not Essential to Nutrition. — The nervous 
system is evidently not essential to nutrition, for this is as 
well effected in the plant as in the animal. This is accom- 
plished in both in substantially the same way. The means 
by which it is done, and its arrangements, are modified, in 
the two cases, to suit the differing circumstances. 

26. Functions of Organic Life and of Ani- 
mal Life. — The nervous system is, for particular pur- 
poses, superadded in the animal to what is common both to 
the animal and the plant, and so constitutes the essential 
difference between them. And so, all the functions rela- 
ting to nutrition, which are common to plants and animals, 
are called functions of organic life. But the functions 
which are performed by the system superadded in the ani- 
mal, the chief of which are sensation and spontaneous 
motion, are termed functions of animal life. These are 
sometimes also called functions of relation, from the espe- 
cial connection which they form between the animal and 
all that is around him. 

27 • Thought and Will. — These animal functions, 
sensation and spontaneous motion, imply thought and will. 
The order of action is this : sensation — thought in regard 
to it — action of the will in consequence of thought — 
then, from this action, an impression carried through 
nerves to organs termed muscles — motion in them from 
their contraction. 

This order, however, is not always observed. The first 
link, sensation, may be absent. Thought, without any pre- 
ceding sensation, may prompt the will, and spontaneous 
motion results. The action of the will, too, may be left 
out, or may be in opposition. Thus, emotions may produce 
action of the muscles, the will not concurring, and perhaps 
opposing ; as when we laugh at what is ridiculous, or weep at 
what is sad, in spite of restraining efforts dictated by the will. 



MAX IX HIS RELATIONS TO NATURE. 1.') 

VS. Chemical Constituents.— One more important 

distinction between animals and plants remains to be no- 
ticed. Organized Bubstances are composed mostly of four 
elements — oxygen, hydrogen, nitrogen and carbon. Plants 
differ from animals, in having but little nitrogen in their 
composition. It was formerly supposed that they contained 
none of this element. It is found only in particular parts 
of plants, as the seeds. We may regard carbon as the most 
characteristic constituent of vegetables, and nitrogen of 
animals. And in this connection it is interesting to observe 
that, while carbon is largely thrown off from the lungs of 
animals, in the shape of carbonic-acid gas, it is as largely 
absorbed by the leaves of plants. Of this fact more par- 
ticular notice will be taken when the subject of respiration 
is reached. 



CHAPTER III 



MAN IN HIS RELATIONS TO THE THREE KINGDOMS 
OF NATURE 

89« Peculiar Endowments of Man. — Man is 

commonly spoken of as being at the head of the animal 
kingdom, and in the book of the naturalist is made an 
order of the class termed Mammalia, As the basis of the 
whole classification is mere material organization, and has 
no reference at all to mental or spiritual endowments, the 
classification, in regard to man, is in its principle correct. 

At the same time, it must bo admitted, that it fails to 
recognize altogether the essential distinctions between man 
and other animals. These distinctions, making, as they do. 
a wide gap — "an impassable chasm," as Professor Gnyol 
expr "ii man and the inferior animals, arc to 

be found in certain peculiar spiritual endowments which 
man pose 



1± PHYSIOLOGY AND HYGIENE. 

30. Abstract Reasoning. — One of these endow- 
ments is the power of abstract reasoning. Other animals, 
in a certain sense, reason, that is, they make inferences; but 
they never arrive at any general or abstract truths. 

31. Conscience. — Another endowment is a moral one, 
linking man in his spiritual nature to the Deity : this is 
conscience, or the knowledge and sense of what is right, in 
distinction from what is wrong. Other animals, in obedience 
to the passions of fear and love, sometimes appear to the 
superficial observer to have an idea of what is right, as 
such; but there is not the slightest evidence that they 
really have any such knowledge. 

32. Immortality. — The force of this view of the 
subject is enhanced, if we take into consideration the great 
fact, revealed to us by God in his Word, that man is des- 
tined to immortality. It may be objected that, as this fact 
is learned only by revelation, and not by observation, it is 
not to be regarded as a scientific fact. 

But, granting that there is truth in the objection, it cer- 
tainly is allowable to allude to the revelations of Scripture, 
as confirming or enforcing views developed by scientific ob- 
servation. The view here presented is based upon endow- 
ments that are recognized by the scientific observer, with- 
out the aid of revelation ; and we can appeal to the revealed 
fact of man's immortality, as adding force to this view, and 
not as being at all necessary to the establishment of its 
truth. 

33. Real Relation to the Animal Kingdom.— 
The grand essential distinction between animals and plants 
lies, as you have seen in the last chapter, in the fact that 
animals have a nervous system. Now, with this system, as 
you have also seen, appear certain mental manifestations. 
These differ widely in different animals, and are most 
prominent in those in which this system is most prominent 
and complicated. As we trace upward these complications, 
when we come to man, we find certain mental manifesta- 
tions, which separate him by " an impassable chasm " from 
all other animals. 



MAN IX HIS RELATIONS TO NATURE. 15 

Till we arrive at him, the difference is, for the most part, 
one of degree. But in his ease it is a difference of kind, 
and a very wide one. Of such a difference the naturalist 
should certainly take very distinct cognizance; and, if it be 
not consistent for him to do so in his classification, great 
force and prominence should be given to these views in his 
instructions on this subject. As the superadding of the 
nervous system separates the animal from the plant, so, 
also, as Professor Guyot very justly maintains, the super- 
adding of such endowments as we find in man separates 
him, by a chasm quite as " impassable," from other ani- 
mals. 

34. Tike Hm id of JIan. — The distinction commonly 
received as the ground of classification for man, is a trivial, 
perhaps a questionable one. He is said to have two hands, 
and so makes the order Bimana ; while apes and monkeys 
are said to have four hands, and are, therefore, considered 
as making the order Quadrumana. 

Now, if Ave observe carefully and fully the wonderful en- 
dowments of the human hand, we shall hardly be willing to 
allow that the monkey has four such members. With a full 
view of the capabilities of the human hand, that of the 
monkey can not be considered as a hand, but as a member 
j- some of the properties of both hand and foot. 

Hands arc given to these animals to enable them to climb 
with facility, and to grasp their food; but they have none 
of that great variety of motion, which is so striking a pe- 
culiarity of the hand of intelligent man. The ground upon 
which they are said to have four hands is that which is thus 
ed by Ouvier. -That which constitutes the htmd, 
properly so called, is the faculty of opposing the thumb to 
the other ii i as to seize upon the most minute ob- 

.*' No animal besides man has this arrangement, ex- 
cept the Quadrumana. It is claimed, therefore, that they 
have hands, although they arc very imperfect when com- 
pared with the hand of man. The imperfection is indeed 
80 great, a- i<> make us at least reluctant to admit the claim 
set up by the naturalist. 



16 PHYSIOLOGY AND HYGIENE. 

35* Views of Dr. Carpenter.—" While/' says Car- 
penter, " the thumb in the human hand can be brought 
into exact opposition to the extremities of all the fingers, 
whether singly or in combination, in those Quadrumana 
which most nearly approach man, the thumb is so short, 
and the fingers so much elongated, that their tips can 
scarcely be brought into opposition, and the thumb and fin- 
gers are so weak, that they can never be opposed to each 
other with any degree of force. Hence, although admirably 
adapted for clinging round bodies of a certain size, such as 
the small branches of trees, &c, the extremities of the Quad- 
rumana can never seize any minute object with such pre- 
cision, nor support large ones with such firmness, as are 
essential to the dextrous performance of operations for 
which the hand is admirably adapted." 

36. Chin, JEreet Posture, Man's Weeping and 
Laughing* — Man's structure differs in many respects from 
that of the inferior animals. It would make this chapter too 
long to point out all the differences. As an example of the 
latter, no animal but man has a chin. Every other animal 
has its lower jaw retreating from the teeth, instead of pro- 
jecting forward below, as in man. 

One of the most important and striking peculiarities of 
man's structure is that general arrangement which enables 
him to be in the erect posture. No other animal naturally 
assumes this posture, or is able to maintain it for any length 
of time ; and most animals assume one which is entirely the 
opposite of this. Even the monkey, when taught by man 
to stand and walk, is by no means erect, but his lower limbs 
are crooked, and the moment that he escapes the necessity 
of being an imitator, he is on all fours. 

There is a distinction of an interesting character, which 
concerns both the nervous and muscular systems. It is this, 
that no animal but man can shed tears, or perform those 
muscular motions which are necessary to the acts of weep- 
ing and laughing. In view of this marked distinction, man 
has sometimes been designated as " a laughing and crying 
animal." 



THE BONES. 1 ? 

37. T/te Essentia/ Distinctions. —But the great 
essential distinctions, to which all the rest are really 
tributary, are, as has been stated, of a mental or spiritual 
character. And these should always be made peculiarly 
prominent, whenever the distinctions between man and the 
inferior animals are treated of by the naturalist. This 
should be done, not only because they are essential, but also 
because all other distinctions are subordinate and tributary 
to them. It is the mental peculiarities of man, for the most 
part at least, that render necessary those peculiarities which 
distinguish his organization from that of other animals. 



CHAPTER IV. 

BONES, 

38. Structure of Bones. — From the osseous or 
bony tissue, the solid part of the framework of the body is 
made. Bone is composed in part of animal matter, and in 
part of mineral. The mineral part is mostly phosphate of 
lime. These two parts of bone are in different proportions 
to each other in the different periods of life. 

39. Mineral Hatter. — The mineral part in the 
child is about one half of the bene; in the adult, four- 
lifths ; and in the old, seven-eighths. Bones are, therefore, 
very brittle in old age, while they are somewhat yielding in 
childhood. The mineral and the animal portions of bone 
can be separated from each other. If a bone be put into 
diluted muriatic acid, the mineral part will, after a time 

•me united with the acid, and the animal part will be 

. having the perfect shape of the bone. Thus separated 

from the mineral part, it is bo flexible, that it can be tied 

into a knot. On the other hand, by subjecting a bone for 

some time to the action of heat, the animal part can be re- 

1, and the mineral part be left by itself. 



18 PHYSIOLOGY AND HYGIENE. 

40. Animal Matter. — The animal part of bone is 
cartilage, or gristle. This part is formed first, constituting 
a sort of mold, in which the bone is to be formed. The 
mineral matter is gradually deposited in the cells of the 
cartilage. In the very young child, you can see that this 
process is not completed, especially if you observe the bones 
of the head. The bones are not united together, as they 
are in the adult, and there is so little of mineral matter 
near their edges, that they can be bent with a very slight pres- 
sure. The proportion of mineral matter which is deposited 
in the cartilaginous bones varies much in different animals. 
In many fishes, there is almost none of this deposit, the 
skeleton retaining its cartilaginous character throughout 
life. 

41. Cartilages. — Besides the cartilaginous portion of 
bones, there are cartilages which are destined to remain so, 
instead of having mineral deposits made in their cells. 
The ends of the bones are tipped with them. They are 
placed between the bones of the spinal column. They also 
form the connecting links between the breast-bone and the 
ribs. Cartilage constitutes the body of the outer ear, of 
the eyelids, and of the lower part of the nose. The trans- 
parent part of the eye is formed of cartilage. This sub- 
stance is placed wherever firmness and tenacity are required 
without hardness. 

42. Function of Hones. — The bones furnish the 
points of support and attachment for the muscles which 
move the different parts of the body. They are, therefore, 
the passive instruments of locomotion. They are united 
together by ligaments of various degrees of strength, ac- 
cording to the necessity of the case. 

The bones, forming the framework of the body, not only 
furnish points of support and attachment to the muscles, 
but in many cases serve to defend important organs from 
injury. Thus, the soft brain is thoroughly secured from 
harm by being inclosed in the skull ; and the lungs are sur- 
rounded by walls of bone so arranged that, while they 
defend the lungs from external violence, they secure a 



THE BOXES. 



19 



Fig. 2. 



wide range of motion for the necessary expansion of these 
organs. 

43* Structure of Bones. — There are some points 

of interest in relation to the structure of bone and its 
growth. It has been stated that bone is generally formed 
in cartilage, the cartilage being formed first as a mold for 
the bone. Bone is deposited in two forms, solid and cellu- 
lar. In the fiat bones, as in the skull, the cellular struc- 
ture lies between two plates of solid bone. In the long 
bones the cellular part is at the two ends, and is covered 
with a thin plate of solid bone, while the shaft is a hollow 
tube with the bone very much condensed. This arrange- 
ment is seen in Fig. *2, representing 
the thigh-bone and the bone of the 
arm. 

44. Hollow Cylinders. — 
Certain well known mechanical prin- 
ciples are observed in this arrange- 
ment. The bone would be unneces- 
sarily heavy if it were solid through- 
out. Lightness in a moving limb is 
of considerable importance. At the 
same time strength is to be carefully 
provided for in a bone which is to 
sustain the weight of the body, and 
to which the large muscles of the 
thigh are attached. By having the 
bone hollow, both of these objects, 
lightness and firmness, are secured. 

The principles involved are recog- 
nized by the architect in the con- 
struction of pillars, and we see them 
exemplified in the hollow stall 
plants. The hollow pillar has 'more 
stren_ quantify of 

matter would have if in one compa 
mass; and the stalk which support 
the full clusters of grain, would break under its load as it 




20 PHYSIOLOGY AND HYGIENE. 

moves back and forth in the wind, if it were solid instead of 
being hollow. 

But the round cavity of the shaft of the bone does not 
extend to the ends. These are necessarily large, in order to 
present broad surfaces for articulation with the neighboring 
bones ; and strength and lightness are secured in this case 
by a cellular arrangement of the body matter, the outer 
plate of solid bone being conparatively thin. There is 
obviously more firmness in the resistance to shocks or pres- 
sure, secured in this way, than there would be if the bony 
matter were all consolidated into a shell containing a cavity. 

The round canal in the shaft and the cellular structure 
at the ends are filled with an oily substance called marrow. 
This, like all other fatty substances, is contained in fat-cells. 
The marrow is also present in the cellular structure be- 
tween the plates of the flat bones. The cavities and the 
cells in bones have blood-vessels, branches of arteries 
and veins that enter the body of the bone at some particu- 
lar points, in the long ones, near the middle of the shaft. 

45. Covering of the Bones. — It is from these blood- 
vessels, together with those that come from the membrane 
investing the bone, called periosteum, that the bone is nour- 
ished. But, although an artery runs through the body of 
the bone, to branch out upon the walls of its cavity, none 
of its branches enter the very substance of the bone. 

46. Groivth of Bone. — The manner in which ma- 
terial is carried to every point of the solid bone has been 
developed by the aid of the microscope. If we cut across 
the solid portion of bone, and examine it with a micro- 
scope, we see here and there orifices of certain minute 
canals that run lengthwise of the bone. 

These canals are found to communicate with the cavity 
of the bone and receive therefore blood, or some of the con- 
stituents of the blood, from the blood-vessels which are 
situated there. These orifices, as seen under the microscope, 
are represented in Fig. 3. Around these orifices a a, you 
see little dark spots arranged in rings, with lines running 
to them from the orifices. By magnifying the section of 



THE BOXES. 21 

bone still more, we see what these spots and lines are. The 
dark spots are small cavities, and the lines are minute tubes 
running to them. In Fig. -4 is a representation of this ar- 
rangement as seen in a little portion of the section of bone, 
more highly magnified than it is in Fig. 3. The tubes pass 

Flo. 3. 






j~ 






© * , 



"iff/ -• "V 



I5& 1 



arr 



I _ ■ 

SECTION OF BONE. 



- a 




out from the canals to the rows of cavities which are around 
the canals, and thus a circulation is kept up at every point 
of the solid bone. It is supposed that the blood itself does 
not circulate in these little channels and cavities in the 
Bolid bone, but a fluid containing the constituents of bone. 
For these channels are too small even to admit the cells 
which the microscope shows us swimming in the blood. 
The fluid that circulates in them is selected from the blood, 
which is contained in the blood-vessels in the cavity of the 
bone, and in the periosteum that envelopes it, 

47. Bones not Sensitive. — It is a very common 
popular notion, that the bones are endowed with great sen- 
sibility, and especially the central part, the marrow. But 
they have in their healthy state no perceptible sensibility, 
and the Bawing of the bone in amputation occasions no 
suffering. When, however, a bone becomes inflamed, severe 
pain is one oi the symptoms. If it were not bo, disease 



22 



FKOJSTT VIEW OF THE SKELETON. 



Fig. 5. 

The Skeleton consists of 
201 bones. In this enumera- 
tion the teeth, the hyoid 
bone, and the bones of the 
ear are not included. Certain 
bones in the sutures of the 
head, and in some of the 
joints, which, though gen- 
erally present, are not re- 
garded as essential parts 
of the framework, are also 
omitted. 

NAMES AID CLASSIFICATION OF 
THE BONES. 



a The frontal bone, . . 1 
b The parietal bones, . . 2 
e Occipital bone, (Fig. 6) 1 
c The temporal bones, . 2 
+ The sphenoid bone, . 1 
t The ethmoid bone, . . 1 

t The nasal bones, . . 2 

t The lachrymal bones, . 2 

/ The upper maxillary 
bones, 2 

g The malar bones, . . 2 

t The palatine bones, . 2 

t The lower spongy 
bones, 2 

t The vomer, .... 1 

h The lower maxillary 
bone, ....... 1 

The bones whose names are 
marked t cannot be shown 
in the fige . 




Skeleton 



BACK VIEW OF THE SKELETON. 



23 




Fig. 6. 

/ The vertebrae, . 24 

o The sternum, . 3 

o' The ribs, . . 24 

Fig. 5. m The ossa inno- 

niinata, . . 2 

/ The sacrum, . 1 

** k The coccyx, . 1 



i The scapula, . 2 

g The clavicle 2 

Fig. 5. i f The humerus, . 2 

y The ulna, . . 2 

z The radius, . . 2 



a' The carpal 

bones, ... 10 

1/ The metacarpal 
bones, ... 10 

c f The phalanges, 28 



1 



W The femur, 

p' The tibia, . 

f The fibula, 

V The patella, 

g' The tarsal bones, 14 

h' The metatarsal 

i' The phalanges, 28 



2 


CD 




V 










2 


£ 




o 






1 


H 




W 


9 


■ 




£ 



Skelp;ton. 



24 PHYSIOLOGY AND HYGIENE. 

might go on to produce disastrous results in a part so 
covered up by others, without any warning of the danger 
of the case. 

48, Shape and Place of Bones. — The bones are of 
every variety of shape, to suit the various offices which they 
are to fulfill. You will see this to be true, as you cast your 
eye over the skeleton as represented in Fig. 5. You first 
observe the somewhat round box of bones, which contains 
the brain, and at the same time furnishes sockets for the 
eyes, extended irregular surfaces for the apparatus of smell- 
ing, and for that of the taste, a place for the organs of hear- 
ing, and at its lower part, in connection with the lower jaw, 
a mill for grinding the food. Then you observe the many 
bones of the thorax or chest, containing and protecting the 
heart and the lungs. 

49. Spinal Column. — The spinal column, f, com- 
posed of twenty-four bones, you see as a firm but movable 
pillar, extending the whole length of the body, and having 
its base firmly planted upon that stout thick bone, the 
sacrum,, which is wedged in so tightly like the key-stone of 
an arch, between the broad spreading bones on either side. 
To this pillar are strongly fastened the walls of the chest ; 
and from the chest thus supported by the spine hang the 
lax front and lateral walls of the abdomen. 

SO. ' Pelvis. — Then below you see the pelvis, as it is 
called, — a set of large bones so arranged in a bowl-form, as 
to offer a broad surface of support to the contents of the 
abdomen. The bone called the ilium, m and I, on either 
side, with its flaring upper surface, is especially serviceable 
in this way. The pelvis also furnishes a socket for the 
round head of the thigh bone s, and points of attachment 
for the large muscles that move the lower extremity. 

51. Bones of the Loiver Extremity. — Observe 
the large bones of the thigh and leg, intended to give firm- 
ness to the lower extremity, and the lighter bones of the 
arm and forearm, fitted for extent and quickness of motion. 
Finally- notice the numerous bones which enter into the 
structure of the hand and the foot. These bones, together 



THE BOXES. 25 

with the intervening cartilages, give them great elasticity 
and variety of motion. 

We notice with some particularity some of the bones, of 
which has been given a general description, as they are 
united together to form the whole skeleton. "We can not 
notice them all, nor dwell upon every point of interest, for 
this would require much more space than can be devoted 
to the subject. We therefore select those points which can 
be made most clear and interesting. 

&2* Skull. — Your attention is first called to the bones 
of the head, as you see them in Fig. 6. There are twenty- 
two bones in the whole head. Fourteen of these belong to 
the face, while eight belong to the cranium ; that is, that 
part of the skull which incloses the brain. Of these, no- 
tice particularly the large bone in front called the frontal 
bone, a, making the forehead, and below forming the upper 
portion of the orbits of the eyes ; the parietal bone, i, the 

Fig. 6. 



BOXES OF THE HEAD. 



upper lateral part of the dome of the skull ; and c the tem- 
poral bone on which the parietal bone rests. There is a large 
bone in the rear forming the back of the cranium as the 
frontal bone does the front. There are also two bones in 
8 



26 PHYSIOLOGY AND HYGIENE. 

the base of the cranium which are out of sight in this view 
of the skull. You may, perhaps, be disposed to inquire why 
this box for holding the brain, should be made of so many 
bones. 

One reason is, that the enlargement of the skull from 
infancy to adult age is effected more easily and better than 
it would be if the cranium were one bone. Another reason 
is, that even in the adult, in whom these bones are at length 
so tightly united, violence is less apt to produce injury, 
from the giving, as it is expressed, of the bones upon each 
other, than it would be if one bone made the whole struc- 
ture. And this is especially true of the child, in whom the 
bones are very imperfectly united. Hence it is that the 
frequent falls of children upon their heads so seldom do 
any injury. 

53. Structure and Union of the Skull Bones. 
— The principal bones of the head are composed of two 
solid plates, while the bony matter between these plates is 
arranged in a cellular or sponge-like form. The outer table 
or plate (for both of these terms are used in relation to it) is 
rather rough, and in some parts has ridges for the attach- 
ment of muscles. But the inner plate is very smooth 
on account of the soft delicate organ that is contained in 
the cranium. It is so brittle that it has been called the 
vitreous table, from its resemblance to glass in this respect. 

The modes of the joining of the bones differ in the two 
tables. In the outer table the joining is by a minute dove- 
tailing, called a suture. Numerous little projections from 
one bone fit accurately into corresponding spaces in the 
edge of the other. This is very well represented in Fig. 7, 
in which you see the sutures on the top of the skull ; b be- 
ing the suture which is formed between the two parietal 
bones ; a, a, that between the parietal and the frontal bone in 
front ; and c c, that between the parietal and the bone which 
forms the back of the cranium. A better joining for bones 
of such a shape as these have, can not be conceived of. But 
the inner table is joined differently. It is so brittle that 
the small projections of the dovetailing mode of joining 



THE BOXES. 27 

would not answer here, for they would break very easily. 
The joining accordingly is in this case by smooth accurately 
fitted edges, somewhat beveled, so that one slightly overlaps 
the other. 

The upper part of the cranium is in the shape of a dome, 
and is constructed upon the same principles as such struc- 

Fig. 7. 




STRUCTURES IN THE SKULL. 

tures are as regards resistance to pressure or violence. As 
in domes that are built by man, so in this dome of the 
cranium, great strength is secured around the lower part, so 
as to resist outward lateral pressure. In the dome of St. 
Paul's there is a double iron chain around its base for this 
purpose, of course concealed from view. In the head of man 
the dome may be considered as composed of the frontal bone 
in front, the parietal bones at the side, and the occipital bone 
in the rear. In front, the base of the dome is strongly forti- 
fied, in the heavy arches that form the upper part of the 
of the eyes, and on the jutting edges of which are 
the eyebrows. In the rear the base of the occipital bone La 
?ery thick, and is fortified with ridges which furnish attach- 
ment to the larg»* muscles in the back of the neck. 



28 PHYSIOLOGY A^D HYGIENE. 

But the most marked and interesting contrivance for the 
strengthening of the base of this dome is at the side. It is 
where the parietal bone b, as seen in Fig. 6, is joined by the 
temporal, c. The joining here is not by suture, for that 
would afford no resistance to lateral pressure, either out- 
ward or inward. To secure this object, the lower bone, 
the temporal, laps over the upper, the parietal, with a bev- 
eled edge. It abuts upon or against it. It has the relation 
to the parietal of a buttress to an arch. 

When great pressure is made on the top of the head, as 
when a heavy load is carried there, there must be a ten- 
dency to outward lateral pressure at the base of the dome 
of the cranium. This pressure is effectually resisted by the 
temporal bones acting as buttresses. The same thing is 
true, also, when a blow is inflicted on the top of the head. 
And if a blow be received at the side of the head, on the 
temporal bone, it is evident that the bones will not be so 
apt to be fractured and pressed inward upon the brain, as 
they would be, if they were united by suture. 

54. Protection to the Brain. — You are now pre- 
pared to see, to what extent the brain is guarded against 
the effects of violence inflicted upon the head. These 
effects come either from fracture of the bones, or from 
concussion without fracture. In either case the vibration 
of the parts concerned is the cause of these effects. The 
guards of the brain defend it from injury, by lessening or 
diffusing this vibration. And it is to be observed, that 
when vibration passes from one texture to another, it loses 
some of its force in the change. 

No two substances vibrate just alike ; and when a vibra- 
tion in one is communicated to another, it is modified, and 
is therefore lessened. Some substances modify and lessen 
vibrations communicated to them more than others do. If 
you apply these principles to the effects of violence on the 
head, you at once see that the brain would be much more 
apt to receive a dangerous shock from the vibration occa- 
sioned by a blow, if its coverings were condensed into one firm 
and thick layer of substance, than it is now. So also, if the 



THE BOXES. 29 

bones of the head were in one solid layer, instead of having 
two layers, or plates, with the spongy structure between, 
and the integuments were all consolidated into one thick 
substance, there would be much more liability to fracture 
than there is with the present arrangement. 

Observe now how many, and how various are the textures, 
through which the vibration of a blow must pass, before it 
reaches the brain. Outside of the bone there is first the 
hair; next comes the skin; then there is the cellular mem- 
brane containing some fat ; then a muscular coat ; and 
lastly, the lining membrane over the surface of the bone. 
These various textures must deaden very much the force of 
a blow, and especially the outer cushion of hair, and those 
inner cushions, as we may call them, of fatty cellular mem- 
brane and of muscle. Then, when the vibration reaches 
the bone, it is lessened by the two plates with the interven- 
ing cells, and there is diffused largely among the many 
bones that unite with the one on which the force comes. 
Then as the shock goes into the brain, it is still farther 
lessened by the membranes which cover that organ. These 
greatly diminish the vibration, precisely as a coating of 
leather on the inside of a bell would deaden its vibration 
when produced by a blow upon the outside. With all these 
provisions the result is, that comparatively few of the blows 
received by the head do harm. 

55* Protection at Particular Points.— There 
are some especial guards at particular points in the cranium, 
where there is much liability to exposure to violence. 
Thus, as the lower part of the frontal bone, where the eye- 
brows are, is especially exposed, the distance from the sur- 
face to the brain is made considerable by an intervening 
chamber in the bone, called the frontal sinus. This sinus, 
which varies much in size in different individuals, is lined 
with a membrane, and communicates with the nose. You 
that this arrangement is a great protection to the 
at that point The outer plal • could be broken, and 
the inner remain uninjured. 

But the protection which this arrangement affords, is no< 



30 PHYSIOLOGY AND HYGIENE. 

confined to that single point ; it serves also to deaden the 
vibration of a blow received by any part of the forehead, or 
by the forehead as a whole. The side of the head, too, is 
peculiarly exposed to blows. And, therefore, the skull is 
peculiarly guarded at this point. Beside the overlapping 
of the temporal bone upon the parietal, to which allusion 
has been made, the parietal bone is made thicker at its 
lower part, where it is most liable to be struck, than it is in 
most of the other parts of it. 

Then, too, the place of joining of the temporal and parie- 
tal bones is covered over by a thick muscle, the contractions 
of which you can feel if you press your fingers upon the 
temple while moving the lower jaw as in eating. This 
cushion of muscle is of great use in breaking the force of a 
blow received in that quarter. 

56. Protection of Organs. — The cranium not only 
contains and protects' the brain, but it at the same time 
serves various other purposes, and protects other important 
organs. The tender and delicate eye has there a bony socket 
with jutting prominences all around it, to guard it against 
violence. The exceedingly minute and complicated appa- 
ratus of the hearing is also carefully protected by the skull, 
and the most important part of it is furnished with wind- 
ing and intricate apartments, halls of audience, in that part 
of the temporal bone which is so hard, that it is called the 
petrous or rock-like bone. To the bones of the cranium 
are attached in various ways, the fourteen bones of the 
face. All these, with the exception of the lower jaw, are 
immovable. The two principal of them are the upper jaw 
bone, and the cheek bone. The former makes with its 
mate of the other side the forward portion of the roof of 
the mouth, the palate bones making its rear portion ; and 
it furnishes the sockets for the teeth. It also at its upper 
part makes nearly the whole of the floor of the orbit of 
the eye. 

The cheek-bone forms the outer lateral part of the 
socket of the eye, and sending back a process or projection 
to unite with one from the temporal bone, c, Fig. 6, forms 



THE BOXES. 



31 




the zygoma or arch, inside of which the temporal muscle 
passes down to be fastened to the lower jaw. The bones of 
the nose make quite a complicated series of cavities, for the 
purpose of presenting, in the mucous membrane, which 
lines them, a large surface, over which the nerve of smell 
is expanded. 

A representation of these cavities is given in Tig. 8; it 
which a is the mouth ; b, the 
opening into the nostril ; d, a 
part of the base of the skull ; c 9 
die communication of the nos- 
tril with the back of the throat ; 
c, the curtain of the palate ; ?, 
the frontal sinus; m 9 another 
large sinus ; g, i, h, spongy 
bones projecting into the cavity 
of the nostril. There is a large 
sinus, that is not seen in this 
figure, which lies over the teeth 
in the jaw-bone. The different 
sinuses are lined with the mu- 
cous membrane extending into them from the nose. 

These, with the spongy bones, make a very large extent of 
surface in the cavities devoted to the sense of smell. The 
branches of the nerves of smell enter these cavities, to be 
distributed over thin walls, through many small openings 
in a bone in the roof of the nose, giving it a sieve-like 
appearance. 

The lower jaw is a bone shaped something like a horse- 
shoe, with its ends turned considerably upward. It has 
two smooth projecting surfaces which articulate with two 
corresponding shallow cavities in the temporal bone. Its 
prominence at the lower part in front, the chin, is peculiar 
to man. there being no such prominence in any other ani- 
mal. The lower jaw ha- sockets for the teeth, and it is so 
. and is so provided with muscles, tli;it these 
teeth can be brought to bear against the teeth of the upper 
jaw in cutting and grinding motions. 



INNER BONES OF THE NOSE. 



32 



PHYSIOLOGY AND HYGIENE. 



Fig. 9. 



57. The Teeth . — The teeth are very nearly like the 
other bones in their structure, but differ from them in some 
particulars. Every tooth has in it three distinct structures, 
which differ in hardness, for reasons which will appear clear 
to you as we proceed. The dentine or iyory constitutes the 
body both of the tooth and of its fangs. In the body of the 
tooth there is a coating of that very hard substance, the 
enamel, over the whole surface of the ivory. This is 
thickest over the top of the tooth, and grows thinner on the 
sides till it is entirely gone where the gum begins. The 
ivory in the fangs has a coating of a very different character^ 
called the cementum. It is not hard like the enamel. This 
arrangement is represented in Fig. 9. This is a tooth with 
two fangs or roots ; 1, is the enamel ; 3, the dentine or 
ivory; 2 and 7, the cementum; 4, an unnatural enlarge- 
ment of the cementum, making an 
excrescence ; 5, the cavity of the tooth 
supplied with blood-vessels and nerves 
which come through the channels 
that you see running up the middle 
of each fang. 

This cavity is analogous to that 
which is found in the shafts of the 
long bones as seen in Fig. 2. The 
Ivory and the cementum are seen by 
the microscope to be very different 
textures. The ivory is traversed by 
innumerable branching tubes run- 
ning from within outward towards the 
cementum, as represented in Fig. 10. 
This is a section of a small portion of 
the dentine and cementum in the 
fang of a tooth, very much magnified, 

a, a, being the dentine, and c, c, the cementum, evidently a 

different structure. 

58. Difference between Bones and Teeth. — A 
tooth differs from a common bone in one important par- 
ticular — when once formed it is never altered in its size. A 




Vertical 
SECTION OF A TOOTH. 



THE BOXES. 



33 



bone grows with the growth of the other parts of the body ; 
but a tooth, when it first protrudes through the gum, is as 
large as it ever will be. The reason of this is, that so hard 

Fig. 10. 




a substance as enamel can not be made changeable as bone 
is. Its hardness is inconsistent with anything like circu- 
lation in it, and without circulation there can be no change. 

If the enamel were not needed, and the teeth could be 
composed only of dentine, they could grow as other bones 
do. And if they could grow, one set of teeth might be 
made to answer the purpose. As it is, the second set are 
needed, because as the jaws grow, the first set are neither 
large enough in proportion to the size of the jaws, nor 
numerous enough to fill up the whole space. If the first 
set were to be the only set, when the jaws became of their 
full size, the teeth would lie altogether too small, and would 
be quite separated from each other. Twenty small teeth (the 
number of the first set) in the jaws of an adult, in place of 
the thirty-two large teeth of the second set, would present 
a very odd appearance, besides being incapable of doing the 
service required of them. 

»>. f >. "Bones not belonging to the Natural Skel m 

eton. — Under the lower jaw IS a little bone, called from its 

resemblance to the Greek letter v, the hyoid or u-like bone. 
Its round end is towards the root of the tongue, and its 



34 PHYSIOLOGY AND HYGIENE. 

two free ends reach backward towards the spine. The 
larynx is suspended from it as from a frame, and the mus- 
cles that draw up this bone, draw up the larynx with it. 
It is one of the few bones in the body not directly connected 
with any other bone. The patella, or kneepan, is one of 
these bones. Also the four little bones in the ear, are not 
connected with any other bone. 

60. The Spine considered as a Sinr/le Piece. 
— Pass now to the bones of the trunk of the body. Let us 
first consider the spinal column, or the backbone, as it is 
called in common language, as if it were all one bone. In 
some respects it does act as one, although it is made 
up of twenty-four distinct bones. It is the great pillar of 
the body. As such, it has the head resting on its top, and 
it furnishes support for the walls of the chest, and for the 
muscles which make up the most of the walls of the abdo- 
men. To it also are fastened the mass of intestines in the 
abdomen, and indeed to some extent all the viscera both of 
the abdomen and the thorax. Sustaining, therefore, so 
much weight in so many ways, it stands firmly planted on 
its great pedestal, the strong broad bone of the pelvis, the 
sacrum. 

And this pedestal is supported, as before said, after the 
manner of a keystone, between the lighter spreading bones 
of the pelvis on either side. But while the spinal column 
acts as a strong and firmly supported pillar, it is necessary 
that it should be flexible for the different motions of the 
body. It is therefore composed of twenty-four bones called 
the vertebrce, so that, as in any considerable motion of the 
column as a whole, there is but little motion between any 
two of them, the motion does not interfere with its office 
as a firm pillar. It is most free in its uppermost part, 
the neck ; considerably so in its lower part, the small of 
the back; and it is least free in that part to which the 
ribs are joined. 

You readily see the reasons for this difference in motion 
in different parts of the column. For the varied motions 
of the head there is need of a free movement of the verte- 



THE BOXES. 35 

bra?. Then for the twisting and turning motions of the 
body, you have the free movement at the lower part of the 
column, which is easily provided for there, because there 
are attached to that portion of it nothing but parts that 
are pliable. It is not so with that portion of it that forms 
the supporting pillar of the framework of the chest. There 
is little motion here of the vertebrae, because the joining of 
the ribs to the column forbids it. 

But besides serving as a firm pillar, and as a flexible 
chain, the spinal column also forms a canal or tube in which 
the spinal marrow, one of the most delicate and important 
organs in the body, is securely lodged. This canal extends 
through its whole length, and from the spinal marrow in- 
cluded in this canal, nerves pass out to all parts of the 
body. 

(il. Yevtcbra y and their Union.— In Fig. 11, you 
see a representation of one of the vertebrae ; a, being the 

Fig. 11. 



Fig. 12. 





A SIDE VIEW OF A VERTEBRA. 



A VERTEBRA. 



lorty of the bone ; b, the hole which forms this vertebra's 
part of the canal for the spinal marrow; and c, the spinous 
process. It is these spinous processes that make the row 
of projecting points >c(jn down the length of the back. 
There are six other pr< only four of which you can 

see in the figure. Four of these processes serve to lock the 



30 



PHYSIOLOGY AXD HYGIEXE. 



Fig. 13. 



vertebra with its two adjoining ones above and below, which 
they do so strongly, that there can be no dislocation of 
them without a fracture. Fig. 12 gives a side view of a 
vertebra. 

Strong ligaments bind these bones together, and there are 
very numerous muscles attached to the 
processes, so that this jagged column of 
bones is very thoroughly enveloped in 
softer substances. 

62. Spinal Cord.— In Fig. 13, you 
see the whole spinal column with the 
sacrum on which it stands. It is laid open 
by a vertical section dividing it into two 
halves, so as to show the manner in which 
the bones form the tube that contains the 
spinal marrow. The darkly shaded strip 
through the length of the figure repre- 
sents this tube. It extends, you see, down 
beyond the limits of the column itself 
through the sacrum. It is bounded in 
front by the bodies of the vertebrae repre- 
sented as sawed through from front to rear, 
and by the spinous processes behind also 
sawed in the same way. In this canal you 
see there is a row of little openings, ar- 
ranged just behind the bodies of the ver- 
tebrae. Through these openings, each of 
which is between two of the vertebrae, the 
nerves go out from the spinal marrow. The 
arrangement is such, that the nerves are 
very securely guarded against the hazard 
of pressure in the movements of the ver- 
tebrae upon each other. 

63. Intervertebral Cartilages. — 
You see also that there are spaces between the bodies of all 
the vertebrae. These are filled with cartilages, which vary 
in thickness in different parts of the column, from one- 
quarter to three-quarters of an inch, being thickest in the 



SPINAL COLUMN. 



THE BOXES. 37 

lower part of the back, where the backward and forward 
motion of the vertebrae upon each other is the greatest 

Eacli cartilage is firmly fastened to the two vertcbnv, 
between which it is situated, by the rough surface of the 
body of the bone which you see represented in Fig. 11. 
This arrangement of cartilages is an important provision 
for the motion of the spinal column. It contributes greatly to 
its flexibility. When you stoop forward, all the cartilages 
are compressed, and when you rise up they return to their 
usual size by their elasticity. And besides this, they serve 
to diminish any shock which might otherwise be trans- 
mitted through the column of bones to the head with too 
great force. There is another guard against the injurious 
transmission of shocks to the brain, in the shape of the 
spinal column, the twenty-four bones being arranged, not in 
a straight line, but in a double curve. 

The vibration, communicated upward through the spinal 
column, is thus not only lessened by the elasticity of the 
cartilages, but is also distributed in different directions by 
the curved arrangement of the bones. If the column had 
been made straight, the head would be subject to frequent 
jars in the movements of the body, which would be disagree- 
able and often injurious. 

64. Different Objects in the Arrangement of 
the Spinal Column. — You have thus seen how three 
different objects, apparently incompatible with each other, 
are accomplished in the arrangement of the spinal column. 
To put twenty-four bones together in such a way, that they 
shall form a strong firm pillar for the whole frame, and yet 
they shall make a column or chain flexible enough for the 
various motions of the trunk of the body, and at the same 
time provide, in this column, a secure canal for the rod of 
nervous matter which moves all the muscles of the body, is 
to produce a piece of mechanism which far transcends any 
thing that has ever been contrived by the ingenuity of man. 

6*7. Arrangement of the First and Second 
Vertebrce. — There remains to be noticed one especial 
contrivance in the spinal column. It is at its summit, and 



33 PHYSIOLOGY AND HYGIENE. 

is for the purpose of providing for the free motions of the 
head in various directions, and at the same time securing the 
spinal marrow at that part,from all hazard of pressure from 
these motions. 

These two objects are accomplished in this way. The 
head in moving backward and forward rocks on two smooth 
surfaces on the first vertebra. But when the head moves to 
the right and left, this first vertebra moves along with the 
head on the second vertebra. And there is a tooth-like pro- 
cess that projects up from the second vertebra inside of 
the first, around which this rotary motion is performed. 
In Fig. 14 is represented the first vertebra. J, J, are the 
two surfaces on which the head rests, and rocks backward 
and forward. A is the opening for the spinal marrow. L 
is the strong ligament which confines the tooth-like process 
that projects upward from the second vertebra. In Fig. 15 
is the second vertebra. P is the tooth-like process, around 
which the first vertebra rotates, carrying the skull with it. 
You see it is smaller at its root than at its top. This 
smaller part is bound firmly by the ligament in the first 
vertebra. It is shaped thus to prevent its slipping out from 
the ligament. J, J, are the two surfaces on which the first 
vertebra moves as it rotates around the tooth-like process. 

Fig. 16 shows the two bones together, the tooth-like pro- 
cess being confined in the ring of the upper bone. Special 
pains are taken to make this arrangement secure, that the 
process may not be in danger of pressing upon the spinal 
marrow at this important point. It is thus that the lateral 
rotary motion of the head and the forward and backward 
motion are secured by two joints, just as is done in the 
mounting of a telescope. The difference between the two 
cases is, that in the mounting of the telescope there are no 
difficulties to overcome, while in arranging the mounting of 
the bead, as we may term it, a peculiar contrivance and a 
nice adjustment are needed to prevent injury of a very im- 
portant organ. It is a wonderful contrivance, by which so 
much and so varied motion can be effected in the very walls 
that contain the soft and delicate spinal marrow, without 



THi: BONKS. 



no 



injuring it. You will fully appreciate this, if you observe 1 
the extent and variety o£ the motions of the head and neck 
executed chiefly with the two bones previously described. 

Fig. 1 \ 




5T VERTEBRA. 



Fig. 15 




Fig. 16. 




F. - mid Bac*«Hl 
VERTEBRAE TOGETHER 



SECOND VERTEBRA. 



(id. Vertebra* of the Bird.— In the neck of birds 
there is a contrivance of a different character, for the ar- 
rangement which answers for the motion- required by man, 

obvi luld not .-cur.' the very free motions which the 

bird executes with its neck. As the bird bends its ueck at 
such abrupt angles in all directions, a peculiar arrangement 




40 PHYSIOLOGY AND HYGIENE. 

of the vertebra is necessary, to prevent the spinal marrow 
from being pressed upon. 

The arrangement is a simple, but effectual 
Fig. 17. one. This can be made plain to you by the 

rough diagram in Fig. 17. A, A, are two 
of the vertebra of the neck laid open. B is 
the spinal canal, and C is the spinal marrow. 
You observe that each vertebra is larger at 
its ends than in the middle, allowing at the 
joinings of the bones, where the motion is, 
a considerable space between the bone and 
the spinal cord. 
spinal column Now if each of these bones was of equal 
m Birds. s j Z e throughout, and the spinal marrow 

filled up the canal, you can readily see that 
when any two of these were much bent upon each other, there 
would be pressure upon the spinal cord; and pressure would 
produce palsy, and often destroy life. But with the simple 
arrangement above described, free motion, almost to a right- 
angle in some directions, can be executed without pressing 
on the cord. And besides this, you can see that the cord by 
this arrangement will not be bent at an angle, as the verte- 
brae are, but in a curve, for the spaces in the spinal canal 
at the joinings allow of a lateral movement of the spinal 
marrow at these points. 

67. Vertebrae of Quadrupeds* — In quadrupeds, as 
they have their heads suspended, instead of being supported, 
as in man, upon a column of bones, the spinous processes in 
the neck are very large, and project much, for the attach- 
ment of rtrong muscles which hold up the head and move it. 
There is also attached to these processes, a very stout fibrous 
ligament, commonly called the jmxy-waxy, to assist in sus- 
taining the head. 

68 o Vertebrceof Fishes. — In fishes the spinal column 
is so arranged as to give it great flexibility. In Pig. 18 is rep- 
resented one of the vertebrae of a fish. If you compare it with a 
human vertebra, as seen in Fig. 11, you will see that it differs 
very widely from it. It has no transverse or side processes. 



THE BOXES. 



41 



VERTEBRA 



Fig. 19. 



While the human vertebra has one spinous process that 
projects behind, this has two, t\ t\ one in front and one in 
the rear, or rather, according to the usual posi- 
tion of the fish, one above and one below. The 
body of the vertebra has a cup-like cavity on 
each side towards its neighboring vertel ra. 
When, therefore, two of these vertebrae are 
joined together, their two cnp-like cavities 
make one cavity of the shape of a double cone, 
as seen in Fig. VX 

This is a representation of a section of a por- *f] 
tion of the spine of a fish. The division is 
made so as to cut the vertebra^ into two halves, 
and thus show these cavities. Each one of these 
contains a sac which is filled with a gelatinous fluid. This 
arrangement, which secures very 
great flexibility of the spinal 
column, you can examine at any 
time when you have fish on the 
table. The long spinous pro- 
cesses make the broad framework 
of the animal, to which its muscles 
are attached. 

09. Vertebra? of Reptiles. 
— In reptiles there is still greater 
flexibility of the spine than in 
fishes. This is secured in two 

-. by the great number of the vertebrae, and by a pecu- 
liar arrangement of them. There are three hundred and 
four vertebrae in the boa-constrictor, over three hundred in 
the common ringed-snake, and over two hundred in the rattle- 
snake. The articulations of the vertebrae in reptiles arc with 
a ball-and-socket arrangement. The forward pari bf each 
•bra has a deep cnp-like depression, in which plays a 
id smooth ball from the back part of tin- nexl vertebra 
And as these joints are firmly bound together by ligaments, 
the spinal column is wry strong as well as flexible. In the 




SPINAL COLUMN OF A FISTI. 



42 PHYSIOLOGY AND HYGIENE. 

gracefully flexible neck of the giraffe we have the same 
ball-and-socket articulations of the vertebrse. 

70. Bones of the Thorax. — The breastbone, which 
is flat and of simple form in man, is much larger and less sim- 
ple in its form in some animals. In flying birds it is not only 
broader, but it has a keel-shaped projection for the attach- 
ment of the large muscles used in flight. The clavicle, g, 
Fig. 5 (so called from its resemblance to a key. and com- 
monly called the collar-bone), is attached at one end to the 
top of the breastbone, and at the other unites with a pro- 
cess of the scapula, or shoulder-blade at the top of the 
shoulder-joint. It is a prop to the shoulder, pressing it out- 
ward; and accordingly it is large in those animals the 
movements of whose superior extremities tend to bring the 
shoulders toward each other, while it is very slender, or 
absent even, in those the tendency of whose movements is to 
keep the shoulders apart. Thus in birds the drawing down 
of the wings by the strong muscles would bring the shoulders 
toward each other, were this not prevented by stout 
clavicles. Sometimes a second bone is added for the same 
purpose. 

But in the horse and other similar animals, the pressure 
of the body downwards between the shoulders tends to 
separate them, and here we find the clavicle deficient be- 
cause it is not needed. The scapula, or shoulder-blade, is a 
thin bone with a stout raised spine or ridge running across 
it, and forming by its end the top of the shoulder-joint. It 
is situated differently from any other bone in the body. It 
is imbedded in muscles and has a very free motion. The 
design of this attachment is to give freedom of motion 
to the arm. The scapula is directly connected with the 
skeleton only by its union with the clavicle. 

In Fig. 20 you see the arrangement of the clavicle, scapula, 
and breastbone. C, 0, are the scapulae or shoulder-blades. 
A, is the upper part of the breastbone. B, B, are the clavicles 
fastened to the breastbone at one end, and to the shoulder- 
blade at the other end at E, which is a process of the 
shoulder-blade, making the projecting top of the shoulder- 




43 



THE COLLAR-BONES AND SHOULDER BLADES. 

Fig. 21. 




44 PHYSIOLOGY AND HYGIENE. 

joint. D, is another process of the shoulder which serves 
for the attachment of muscles and ligaments. It is called 
the coracoid process, from its resemblance to the beak of a 
crow. 

71. Bones of the Tipper Extremities. — The 
upper extremity is divided into three parts, the arm, the 
forearm, and the hand. The arm has but one long bone, 
the humerus, % Fig. 5. This has a round head which moves 
in a shallow cup formed by the shoulder-blade. The shal- 
lowness of the socket is the cause of the frequency of disloca- 
tions of the shoulder. But if there were a deep socket like 
that which receives the head of the thigh-bone, the arm 
could not have anything like its present freedom of motion. 
Such an arrangement would involve too much of a sacrifice 
of necessary uses for the sake of security. At its lower part 
the humerus makes a hinge-joint with the forearm. 

The forearm has two bones, the radius, b, Fig. 21, and 
the ulna, a. The peculiar arrangement of these two bones 
is worthy of notice. The hinge-like motion of the forearm 
upon the arm is performed by the ulna alone. This bone has a 
beak-like process, which works over a smooth round surface 
at the end of the humerus. It is the outside of this pro- 
cess which you feel at the point of the elbow. The other 
bone, the radius, has nothing to do with this motion. This 
only rolls on the ulna in the rotary motions of the forearm. 
But at the other end of these bones, at the wrist, the ar- 
rangement is reversed. Here, it is the radius on which the 
hand moves in a hinge-like manner, while the ulna at c rolls 
on the radius, as the radius does on the ulna at the elbow. 

You can readily see that as the radius rolls on the ulna 
at the elbow, and the ulna on the radius at the wrist, a very 
free rotary motion of the forearm is provided for. The 
combination of this motion with the motions at the wrist, 
the elbow, and the shoulder, secures that almost endless 
variety of movement, which is so striking a peculiarity of 
the upper extremity, as compared with the lower. 

The hand is divided into three parts, the carpus, p, Fig. 5. 
composed of eight small bones, the metacarpus, 7, composed 



THE BONES. 



45 



of bones which are like the bones of the fingers, r. The 
eight bones of the carpus are firmly packed together, but 

they have a slight motion upon each other, and this, to- 
gether with the motion of the metacarpal bones, makes the 
hand a more easy, light, and springy instrument than it 
would be, if these bones were all consolidated into one. 
The metacarpal bones are the framework of the flat part of 
the hand, and to them are joined the first row of the bones 
of the fingers. The metacarpal bone of the thumb has a 
very free motion upon the carpus, differing in this respect 
altogether from the metacarpal bones in the body of the 
hand. The bones in the wrist and hand are bound together 
by very strong ligaments. Those which are seen in the 
palm of the hand are represented in Fig. 22. Those which 
you see at a, b, and c bind the small bones of the wrist to- 

Fig. 22. 




gether, and also tie them strongly to the bones of the fore- 
arm, the ends of which you see in the Figure. 



46 



PHYSIOLOGY AND HYGIENE. 



Fig. 23. 



The bone at $, to which so many of these ligaments are 
attached, is the prominent bone which you feel at the be- 
ginning of the palm of the hand on the side towards the 
body. The ligament g connects this bone with the metacar- 
pal bone of the little finger. At d, d, are ligaments which 
running across the hand bind the metacarpal bones to- 
gether at their beginning. At e, e, are similar ligaments, 
where the bones of the fingers join them. The bones of the 
fingers and thumb are strongly held together by lateral liga- 
ments, as seen at /, /. The various 
ligaments of the wrist and hand per- 
mit a slight motion between the bones; 
and thus the hand has freedom and 
ease in its motions while it is also a 
very strong and firm instrument. 

72. Bones of the Lower Ex- 
tvemities. — The lower extremities 
have some resemblance to the upper 
in their structure and arrangement, 
but differ from them in some import- 
ant respects. Here firmness is the 
chief object, while freedom of motion 
is the great thing to be secured in 
the upper extremities. The lower ex- 
tremities are chiefly for locomotion, 
but the upper are fitted for a variety 
of purposes. The body is supported 
upon the lower extremities, and there- 
fore, the thigh-bones have sockets in 
the broad flaring bones of the pelvis m 
and Z, Fig. 5. In Fig. 23, is repre- 
sented a rear view of the thigh-bone. 
Its head, a, is round, and fits into a 
deep socket in the pelvis. 

At b is a depression in which one end 
of a stout short ligament is fastened, 
its other end being attached to the 
bottom of the socket. At c is the neck of the bone; at d 




THE BONES. 47 

arid c are two projections to which are attached large 
muscles to move the limb. Along the shaft of the bone, g, 
there is a rough ridge. h 3 to which muscles are fastened ; j 
and k are two smooth surfaces for articulation with the leg 
below. At t, Fig. o. is the bone called the patella or knee- 
pan, which answers as a defence to the joint, and at the 
same time affords a mechanical advantage, to the muscles 
which throw the leg forward. 

These muscles are fastened to the upper part of the patella, 
and then a connection is formed by a strong tendon between 
its lower part and the large bone of the leg. You see at 
once that the leg can be thrown forward with more force by 
this arrangement, than it could be if the tendon of the 
muscles passed over the front of the joint without any 
patella. 

This will be referred to again in the Chapter on the Mus- 
cles. The leg has two bones, v and u, Fig. 5; but unlike 
those of the forearm they are constructed and arranged for 
strength, and not for freedom of motion. The foot, like 
the hand, is divided into three parts. The tarsus, a, Fig. 24, 
is that part of the foot which extends from the heel to the 
middle of the foot. It is composed of seven bones, the 
largest of which makes the body of the heel. The metatar- 
sus, I, has five long bones reaching from the tarsus to the 

Fig. 24 




The toes, r, have fourteen bones. The object of hav- 
ing so many bones in the body of the foot is t.» give a cer- 
tain springiness to it, which guards against shocks, and 
facilitates motion. Its arched form also tends to Been re the 



48 



PHYSIOLOGY AND HYGIENE. 



Fig. 25. 



same object. In every movement of the foot there is a slight 
motion between all these bones. 

Thus in walking, when the foot first touches the ground, 
it does so at the heel, as represented in Fig. 24. Then as 
the body moves forward, the fore-part of the foot is brought 
down, the weight of the body at length pressing upon the 
ground at the J)all of the foot, b. In executing this move- 
ment, elasticity is given to the tread of the foot by the 
very slight motion which occurs between these many bones. 
If the body of the foot were all one bone it would mani- 
festly be a very stiff and awkward affair, and ease and grace 
in walking would be an impossibility. With such a foot we 
should not walk much better than one does with a wooden 
leg. 

73. Synovial Membrane. — Before leaving the sub- 
ject of the bones, your attention is called to the provision 
which is made for the easy movement of 
their joints. The ends of the bones are 
tipped with cartilage, so as to afford a firm 
but smooth surface for the motion of the 
one bone upon the other. Besides this pro- 
vision, the ends of every two bones that 
move upon each other are lined with a 
membrane, so arranged as to make a blind 
sac. 

This is illustrated in Fig. 25, in which a 
and b are the ends of two bones, the sac, c, 
lying between them represented here as de- 
tached from the bone, in order that the 
arrangement may be clear to you. It is as 
if a small bladder were introduced between 
the two ends of the bones, and were fast- 
ened all over the surfaces that press together. 
The inside of this sac is kept lubricated with a bland fluid 
resembling the white of egg, so that the joint may work 
easily. This fluid is secreted by the membrane itself, and 
the moving machinery of the human system may therefore 
be said to oil its own joints. 




DIAGRAM 

showing the lining of a 
joint. 



THE BONES. 



49 



w 

o 



7- ~ 

hd 

> 
o 
ft 



- - - 
< - ~ - 

- " g a 



5 2 ™ ~ 



o - 



3 3 

it 



00 



Q 

> 

GO 
> 

O 



O 
H 
K 



q r ►< 

3 > - 

S -= 3 

2 i 

1 I 




1=1 

Q0 



o 



Q 

E 

Q 
H 

B 

CO 

H 

♦— i 

o 

GO 






o 
o 

o 

GO 



o 



3 2 



> > 



fc 




GO 

W 

ft 

ft 

O 

I 

W 

o 

% 

ft 

GO 
*H 

O 
i— i 



H 
a: 



50 PHYSIOLOGY AND HYGIENE. 

Ill the knee-joint, the broad surfaces of which are sub- 
jected to so much pressure, there are two flat pieces of carti- 
lage loose in the joint, which operate like friction-wheels in 
lessening the friction. There is a similar provision in the 
articulation of the lower jaw. This member does so much 
work in talking, and such heavy work in mastication, that 
each of its joints has a movable cartilage for the diminu- 
tion of friction. Sometimes when the lubricating fluid is 
deficient, or becomes too thick, a disagreeable crackling 
noise is produced by these cartilages in the motions of the 
jaw. 



CHAPTER V. 

THE MUSCLES, 



74. Structure of Muscles. — Muscular substance is 
what is commonly called the lean meat. It is of various 
colors in different animals, or in the same animal at differ- 
ent periods of life. 

All motion in animals is produced by muscles. They 
act by contracting or shortening the fibrils of which they 
are composed. Commonly there are tendons united with 
the muscles. These tendons are composed of strong white 
fibres, and have no power of contractiou themselves. They 
serve merely as the cords by which the contracting muscles 
move the bones and other parts. 

75. Each Fibril of a Muscle Supplied with a 
Nerve. — Each fibril of which the muscle is composed, is a 
chain of cells, and it is the shortening of all these chains of 
cells in a muscle that produces its contraction. The action 
of a muscle is dependent upon the nerves. Each fibril has 
a nervous fibril or tubulus, by which its connection with 
the brain or spinal marrow is established. And each fibril 
is in this respect probably wholly separate from every other 



THE MUSCLES. 51 

fibril. When, therefore, the mind wills that a certain 
motion shall be performed, an impression is sent to each 
fibril of every muscle engaged in that motion, through the 
tubulus devoted to that fibril. When the action is a very 
complex one, calling into operation many muscles, a multi- 
tude of these impressions are communicated through a mul- 
titude of distinct channels or tubuli. The individual is not 
at all conscious of the compound nature of muscular action, 
and he knows nothing of the muscles which produce any 
particular movement, unless he has studied anatomy and 
physiology. He wills the movement to take place, and at 
once the requisite impressions are sent along the appropriate 
channels or tubuli to their destination. 

These impressions must differ in degree or intensity in 
producing different amounts of motion; and they must 
differ in some cases in different parts of the same muscle, as 
some fibres are put in motion while others are not, or as 
some act with more force than others. 

76. Tendons. — Muscles commonly end in tendons, 
which, as they are white and shining, are quite in contrast 
with the red muscular fibres. The tendons have in them- 
selves no power of contraction, but are mere passive cords. 
They have the same relation to the muscles that ropes have 
to the men that pull them. They are of various shapes, ac- 
cording to circumstances. Long and slender tendons may 
be seen on the back of the hand in thin persons, the muscles 
that pull them being in the full arm above. 

The tendons are not bounded by a distinct line where they 
join the muscles, but tendinous and muscular fibres inter- 
twine, so that they appear to run insensibly into each other. 
Tendinous fibres also mingle in the same way with the 
fibres of bone, making so strong an union, that a great force 
exerted in pulling on the tendon will sooner effect a rupture 
of the tendon or the bone, than a separation of the con- 
nection between them. 

77. Strength and Size of Tendons.— The ten- 
dons ry strong, being made of very condensed fibrous 
substance. The tendon of a muscle is, therefore, much 



52 PHYSIOLOGY AISD HYGIEKE. 

smaller than the muscle itself. This is a circumstance of 
much importance in the arrangement of the moving appa- 
ratus of our frames. The bulky muscles and the slender 
tendons are so arranged, for example, in the limbs, as to 
give them both freedom of motion and beauty of form. The 
muscles that move the fingers help to make up the full part 
of the arm, while their slender tendons occupy but little 
space as they play over the bones of the wrist. If there were 
no tendons, and the muscles were extended to the j arts 
which they move, the hand would be a large cumbrous mass, 
instead of the light and agile thing that it is now. 

78. Action of Muscles. — In the action of the 
muscles upon the bones, we have examples of the three 
kinds of levers treated of in natural philosophy. 

79. First Kind of Lever. — The first kind of lever 
has the fulcrum between the weight and the power, as rep- 
resented in Fig. 26. F is the fulcrum, W the weight, and 

Fig. 26. 




FIRST KIND OF LEVER. 

P the power. You have examples of this lever, in the com- 
mon pump-handle, the beam of a pair of scales, the crowbar, 
as commonly used, scissors, &c. You have an example of 
this form of lever in the human body, in the action of the 
muscles in moving the head back and forth on the top of 
the spinal column. 

In this case, when the head is moved forward, the top of 
the spine is the fulcrum, the weight to be moved is the back 
of the head, and the power is the contraction of the muscles 
that bow the head forward. When the head is bent back- 
ward, the power is the contraction of the muscles behind, 
and the weight is the front part of the head. The muscles 
that move the head backward are stronger than those that 



THE MUSCLES. 



53 



move it forward. It is necessary that this should be so, for 
there is more of the head in front of the point of support 
or fulcrum than there is behind it. Hence, when sleep re- 
laxes the muscles, if we are sitting up the head falls forward. 
<SY). Second Kind of Lever.— In the second kind 
of lever the weight is between the fulcrum and the power, 
as represented in Fig. 37. The common wheelbarrow is an 
example of this form of lever. You have an example of it 
in the body in the raising of the heel from the ground 

Fig. 27. 




SECOND KI^D OF LEVER. 



in walking. In doing this, the weight to be raised is the 
whole body, the foot being the lever, and the forward part 
of the foot being the fulcrum. This will be made clear by 
Fig. 28. W is the large bone of the leg sustaining the 

Fig. 28. 




ght of the body; F, is the ftricrum, the forward part of 
the foot that presses on the ground as the heel is raised; 
and P. is the power at the end of the lever, tie- large mnscle 
in the calf of the leg, that raises the heel. 



54 



PHYSIOLOGY AKD HYGIENE. 



81. Third Kind of Lever. — In the third form of 
lever the power is between the weight and the fulcrum. A 
common example of this is seen in the raising of a ladder. 
The fixed foot of the ladder is the fulcrum, the ladder itself 
is the weight, and the power is applied as far from the ful- 
crum as it can be. Fig. 29 represents a lever of this kind. 

Fig. 29. 




THIRD KIND OF LEVER. 

This form of lever is more frequently used than the other 
forms in the human body. We have an example of it in 
bending the forearm upon the arm as seen in Fig. 30, in 
which 1 is the bone of the arm; 2, the bones of the forearm; 
4, the muscle which bends the forearm upon the arm ; 5, its 
double-headed attachment above ; and 6, its attachment to 

Fig. 30. 




the radius, one of the bones of the forearm. In this case 
the fulcrum is at 8, the joint of the elbow, the weight is the 
hand with whatever it holds, and the power is applied at the 
point where the tendon is fastened to the radius, that is, 
as in the case of the ladder, between the fulcrum and the 
weight. The muscle which straightens the forearm upon 
the arm is represented at 7. 



THE MUSCLES. 55 

82. Time and Power. — In the management of the 
three kinds of levers there are two different objects aimed at, 
under different circumstances. One object is to move a 
great weight with a small power. Here quickness is not 
aimed at, but the weight is moved slowly. The other object 
is to move the weight quickly, an object inconsistent with 
the moving of any very heavy weight. When the object is 
to move a heavy weight slowly, the lever is so managed as 
to get a good purchase, as it is expressed. 

Thus in the case of the lever of the second kind, Fig. 27, if 
the weight be a heavy one, the power is commonly applied 
at some distance from the weight. The nearer the power is 
to the weight, the greater must it be to move the weight. 
The smaller the power, the further must it be from the 
weight. 

But though a small power, if at a distance from the 
weight, answers to raise it, yet in this case the power must 
move through a considerable space to move the weight but 
little : while to raise the weight to the same height, a power 
nearer to it passes through but little space. This will be 
made clear by Fig. 31. F is the fulcrum, and W the weight. 
If the lever. A, be raised to the line B, the dotted lines will 
show the different spaces which the power passes through, 
according to its distance from the weight. If the power be 
at P. it passes through the space indicated by the dotted line 

Fig 31. 




a in moving the weight W to r. But if it be at p y it passes 
through a much Bhorter space, b, in raising the weight to 
the same height The more important, therefore in this 
form of lever, quickness of movement is, the nearer to the 
weight is the power applied. 



56 PHYSIOLOGY AND HYGIENE. 

Let us look at the application of these principles to the 
example of this kind of lever, which was cited from the 
human body, represented in Fig. 28, the raising of the 
weight of the body on the foot in walking. The power 
is here applied quite near to the weight, for quickness 
in raising the heel in walking and running is of great im- 
portance. By having the heel project farther behind, the 
muscle could be attached farther from the weight, and thus 
act with more power. But there would in this case be a 
sacrifice of quickness of movement, and besides this, the 
lengthened heel would present a very awkward and ugly 
appearance. 

But it is in examples of levers of the third kind that we 
find these principles best illustrated. This form of lever is 
much more often used in the mechanism of the muscles 
than the other forms. Eefer to the example given of this 
lever in the action of the biceps muscle in bending the fore- 
arm, as shown in Fig. 30. In this case it is of much more 
importance to move small weights quickly, than to move 
heavy ones slowly. Therefore the power is applied quite 
near to the fulcrum. The tendon of the biceps, as you see, 
is fastened to the main bone of the forearm near the fulcrum, 
the elbow. The point where the power is applied would 
pass through but little space, in moving a weight through 
a considerable one. The lower jaw, in its upward motion, 
is a lever of the same kind. In this case, force, rather than 
quickness, is required in breaking and grinding the food. 
Here, therefore, the power, the action of the muscle, is ap- 
plied farther from the fulcrum than in the case of the biceps 
muscle of the arm, and nearer to the weight to be moved, 
or the point where the resistance is which is to be overcome. 
It is applied also in a different direction — a point which will 
be considered in another connection. 

The muscles which move the lower jaw upward can be 
seen in Fig. 32. One is the large spreading muscle 5, the 
swelling of which, in its contraction, we can feel, if we place 
the fingers on the temple while moving the lower jaw up- 
ward. The other is the short strong muscle c, the front 



Till: MUSCLES. 



:>; 



edge of which is so far forward, that one-third at least of 
the lower jaw-bone is embraced by this muscle. 

Now, if you compare this bone as a Lever, with the forearm 
as acted upon by the biceps, you will at once see that the 



Fig. 32. 




MTJSCLES OF FACE AND NECK. 



power is applied much nearer to the weight, or the resis- 
tance to be overcome, in the case of the jaw, than in the 
of the arm. It is so even when the resistance to be 

come is at the front teetli ; and it is much more so 
when the resistance is at the back part of the mouth, as when 

are grinding our food. Here, indeed, a portion of the 

scalar force is brought to bear upon the resistance in a 
direct line. Ir i< not merely because the back teeth are 

oger than the front ones, but also because the power is 
bearer tip' resistance, that we can crack a nut more «';i>ily 
with the back, than we can with the front teeth. 

83m Mechanical jyisadvantage.—W is clear that 
the biceps muscle acts, as it is expressed, at a mechanical 



58 PHYSIOLOGY AND HYGIENE. 

disadvantage, if we regard mere power or force, and leave 
out of view quickness of motion. If it were inserted further 
down on the forearm, nearer the hand, it could raise much 
greater weights than it now can. A similar statement can 
be made of most of the other muscles of the body. 

But force is sacrificed for the sake of quickness in most 
cases, because the latter is more important. In the few 
cases in which force is the more important, as in the case 
just cited of the lower jaw, the reverse arrangement is pro- 
vided. This gain in quickness can be illustrated by Fig. 33. 
F being the fulcrum, the power in raising the weight, W, 

Fig. 33. 




to c, if acting at P, passes through the space indicated by the 
dotted line a. But if it act at p, it will pass through all 
the space b, and of course raise the weight more slowly than 
when acting at P. 

Most of the muscles work at a mechanical disadvantage 
in another way. Observe the direction in which the muscle 
acts on the bone to be moved. This is seldom at right 
angles, and therefore a considerable part of the force exerted 
is lost. This can be made clear by Fig. 34. Let b repre- 
sent the bone of the arm, and r its fulcrum, or point of 
support in the shoulder. You readily see that if the bone 
be acted on by a muscle, m, at right-angles to it, it will re- 
quire less force to move it to a given point than would be 
required if the same muscle were placed in the position 



THE MUSCLES. 59 

represented by n. For the muscle >?, acting obliquely on 
the bone, would expend a part of its force in pressing the 
end of the bone upward against the socket of the joint at r. 

Fig. 34. 




But in this case also, what is lost in power is gained in 
quickness of movement. This can be shown by the figure. 
We will suppose that the muscle contracts or shortens itself 
half of the length of the tendon. If the muscle were placed 
as at m, the bone would be carried to the line a, c. But 
if the muscle be placed as at n, the same degree of con- 
traction would raise the bone to the line a, d, the point of , 
the bone where the tendon of the muscle is attached moving 
in the curved line as marked. 

It, of course, requires much more power for the obliquely 
placed muscle, n, to raise the bone to the line a, d, than for 
the muscle m, to raise it to a, c; and therefore a much 
larger muscle is needed than there would be if it acted at 
right-angles to the bone as at m. And the muscle which 
raises the arm at the shoulder, acting as it does at so great 
disadvantage, is a very large muscle. The muscle, n, in the 
figure, represents only the line of its action, and not at all 
shape. If you observe the various motions of the arm 
in which this muscle has a part, you will appreciate the 
Bsity of so arranging it as to secure quickness of move- 
ment This was the chief object to be aimed at in its 
arrangement; and the second and less important object, 
power, is secured, so far as it is needed, by simply making 
the muscle a large one. 



GO 



PHYSIOLOGY AND HYGIENE. 



Fig. 35. 




Fig. 36. 



— o 



84. Plan by which the Mechanical Disad- 
vantage is Overcome. — The mechanical disadvantage, 
which was noticed as resulting from the oblique 
action of the muscles, is in part obviated by a 
very simple contrivance. It is done by making 
the tendon of the muscle work over an enlarge- 
ment of the bones at the joints, 

The operation of this contrivance can be made 
clear by Figs. 35 and 36. Let r and o (Fig. 35) 
be the two bones of a joint, and let the muscle 
m be attached to the bone o at u As it contracts, 
almost all its force will be spent in drawing the 
bone o upward against the bone r, because it 
acts almost entirely in a line with the bones. 
But let the ends of the bones be enlarged as in 
Fig. 36, and you see that the direction of the 
tendon of the muscle m is so changed where it 
is attached to the bone, that the muscle can now very 
easily make the lower bone turn upon th^ upper. 

The enlargement then of the bones at the joints, which 
is needed to give the requisite extent 
of surface for working them, answers 
also another good purpose in thus 
altering the direction of force in the 
muscles. In the case of the knee- 
joint there is an additional contriv- 
ance for making this change of 
direction still greater. A movable 
bone, the patella or kneepan, besides 
acting as a protection to the joint, 
effects also the purpose referred to. 

The manner in which it does this 
can be made plain by Fig. 37, in 
which a represents the end of the 
thigh-bone ; 5, the end of the large 
bone of the leg articulating with it ; 
c, the patella ; d, the large tendon which comes from the 
muscle above, and is fixed into the patella; and e, the ten- 



Fig. 37. 




THE MUSCLES. 



01 



don which goes from the patella to the large bone of the leg 
below. The dotted line shows how much the direction of 
the force of the muscle is changed by this arrangement 
The movement performed by this muscle is throwing the 
leg and foot forward, which it is by the above arrangement 
of the patella enabled to do with great ease in walking, and 
with great force in the act of kicking. 

85. The Pulley. — The pulley is used in the arrange- 
ment of the muscles, though by no means so often as the 
lever. It serves, whenever it is used, to change the direc- 
tion of the force. 

At the wrist and the ankle there are broad ligaments 
which bind down the tendons of the muscles, and sustain 
to them the relation of pulleys. If it were not for these 
ligaments the tendons at these joints would fly out con- 
tinually when the muscles are in action, making projecting 
cords under the skin. And if the skin were removed, the 
tendons would be in a position similar to that represented 

Fig. 38. 




at A, in Fig. 38. In this Figure, C is a tendon of the 
great toe in its position as bound down by ligamenta 



02 PHYSIOLOGY AND HYGIENE. 

Now if the muscle were in the position represented by A, it 
is plain that it would act at a greater mechanical advantage 
than in the position ; but the toe would not be moved so 
quickly ; and besides, if the tendons projected in this way, 
the foot would be a very cumbrous piece of machinery, com- 
pared with what it is now, with the tendons bound down 
around the slender ankle. So that both beauty and use are 
secured by the arrangement. 

There is a beautiful application of the pulley in the case 

of the muscle that draws down the lower jaw, called the 

digastric muscle. It is represented in Fig. 39, in which a 

is one end of the muscle attached behind the ear, and b is 

the other end attached to the inside of the lower part of the 

chin. 

Fig. 39. 




DIGASTRIC MUSCLE. 

It is muscular at the two ends, and tendinous in its middle 
part. This middle part runs through a loop or ring in a 
small muscle as represented in the Figure. This little muscle 
is fastened above to a small process of bone under the ear, 
and below to the hyoid, or U-shaped bone, c, which is sit- 
uated just above the larynx. Now when the jaw is to be 
drawn down, the two fleshy ends of the digastric muscle con- 
tract, and the middle tendinous part works in the ring pro- 
vided in the little muscle. This muscle is so slender, that 
its loop is of itself hardly strong enough, as we should 



THE MUSCLES. 63 

suppose, for the tendon of so large a muscle as the digastric 
to work in. And we accordingly find that there is an 
additional security in a strong ligament, which fastens the 
tendon of the digastric muscle to the hyoid bone. 

This ligament (which is not represented in the figure, 
because it would confuse your view of the pulley-action of 
the parts) is sufficiently long to allow of all the freedom of 
motion necessary to drawing the jaw downward. You see 
at once that one object of this arrangement of the digastric 
muscle is to secure beauty of form in the neck. A muscle 
extending from the top of the chest to the chin in a straight 
direction would very effectually draw down the lower jaw, 
but it would be a great deformity. This is avoided by the 
pulley-arrangement of the digastric muscle. 

But this muscle answers another purpose besides drawing 
down the jaw. If, while the jaw be held fast by muscles 
which draw it upward, the digastric contracts, it will draw 
up, as you can readily see by the Figure, the hyoid bone, c, 
and with it, of course, the larynx which is attached to it. 
Now precisely this set of motions occurs when we swallow. 

The mouth is shut by the drawing up of the jaw, and then 
the contraction of the digastric muscle draws up the larynx, 
as you can perceive if you place your fingers on the larynx, 
or Adam's apple, as it is called, when you perform the act of 
swallowing. The little muscle in which the loop is, renders 
some assistance to the digastric in thus drawing up the hyoid 
bone and the larnyx, as you can see by the Figure. 

80. Muscles of the Eye. — There are six muscles 
that move the eye-ball. Five of them are represented in 
Fig. 40. There are four straight muscles, three of which are 
marked a, b, c; the fourth is behind b, only the upper edge 
of it being seen in the Figure. These muscles are, at their 
origin in the back part of the socket of the eye, arranged 
round the optic nerve, and passing forward, are attached to 
the sclerotic coat, the firm white coat of the eye. The two 
lateral muscles, b and its opposite, move the eve to the one 
side and the other, and the two muscles, a and c, perform 
the up and down motions. 



04 PHYSIOLOGY AND HYGIENE. 

But there are certain oblique rolling motions of the eye- 
ball which can not be executed by these straight muscles. 
For these motions two muscles are provided, one of which 
has a pulley-arrangement, as represented in the Figure. 

Fig. 40. 




This muscle, s, has a long tendon which passes through a 
ring of cartilage in the roof of the socket, and then turning 
back is fastened as you see to the upper part of the eyeball. 
This muscle is under the direction of one nerve alone. 

It is an involuntary muscle which performs the insensible 
rolling motions of the eyeball, and like the other involuntary 
muscles of the body, is at work while we are asleep, as well 
as when we are awake. It is the muscle which rolls the eye 
about tremulously when it is open in the insensible state 
sometimes produced by disease. 

87. Opposing Muscles. — Every muscle performing 
a motion has its opposing muscle or muscles, which perform 
the opposite motion. In the case of any two opposing mus- 
cles the one must be in some measure relaxed while the 
other is in action. Thus in alternately bending the elbow, 
and straightening it, there is alternate action and relaxation 
in the two opposite muscles 4 and 7, as represented in Fig. 
30. So in moving the head back and forth the muscles in 
front and rear are alternately contracted and relaxed. 

There is indeed in every muscle some amount of contrac- 
tion which is independent of action through the nerves, 
whether it be reflex, or produced by the will. For this 
reason the muscles cut off in amputation of a limb retract. 
So also if the muscles on one side of the face be palsied, 
those on the other side draw the mouth to that side. The 



THE MUSCLES. 65 

mouth is held in the middle of the face by the equal action 
of pairs of muscles. The head, too, is held in equilibrium 
in the same way. 

In what is called wry-neck, this tonic contraction, as it is 
sometimes termed, is greater in the muscles on one side 
than it is on the other. In some cases a cure can be effected 
only by dividing the contracted muscles. In strabismus, or 
squinting, one of the straight muscles of the eyeball con- 
tracts too strongly for its opposing muscle, and as in wry- 
neck, dividing the contracting muscle is often necessary to 
remedy the difficulty. 

88m Compound Muscular Action. — Most mo- 
tions are not performed by single muscles, but by the joint 
and agreeing action of several, and sometimes many muscles. 
And as these muscles may vary to a great extent in their 
degree of contraction, the motions produced by them are 
nut only compound, but are exceedingly varied. In Fig. 32 
you see a pair of muscles, one of which is marked //, which 
extend from the large protuberances behind the ears to the 
toj) of the breast-bone, 

When they contract equally, the head is bent straight for- 
ward in the middle line between the muscles, and a line 
drawn from the middle of the forehead down to the breast- 
bone would strike exactly at the point where these two 
muscles unite. But if one muscle contracts more strongly 
than the other, the head as its bows forward turns toward 
the side on which is the strongest contraction. And as the 
degrees of contraction in these tw T o muscles may be varied, 
lere may be a variation in the degree of inclination of 
the head to one side or the other, as it is bent forward. 

If then a variety in the direction of motion may be pro- 
duced by variation in the degrees of action in two muscles, 
one can readily see that an almost infinite variety of motion 
must resnlt from this variation, where many muscles are 
called into action. 

Htt. Muscles of the Tongue*— -There is do pari of 

the body which exemplifies in so palpable a manner the 

pound and diversified character of muscular motion aa 



66 PHYSIOLOGY AND HYGIENE. 

the tongue. It is mostly a bundle of muscular fibres, ap- 
parently mingled together in confusion, but really arranged 
in perfect order, so that the tongue can be moved with great 
definiteness in all directions, forward, backward, upward, 
downward, to either side, and in all intermediate directions. 

But all this wonderful variety of movement is produced 
in obedience to the definite action of nerves, whose fibres are 
mingled with the muscular fibres of the tongue. And in 
order to produce each motion there is an agreement of 
action not only between many of these fibres, but also between 
multitudes of them. 

90. View of the Muscles. — The muscles are of vari- 
ous shapes and sizes, according to the motions which they 
are designed to produce, and the circumstances in which 
they are placed. They are round, long, short, flat, fan- 
shaped, circular, serrated, &c. At a (Fig. 41) is the very 
large muscle that makes the fleshy prominence at the upper 
part of the arm, and the office of which is to raise the arm, 
carrying it out from the body; its fibres are not all arranged 
alike, but lie in different directions. The result is, that 
while the arm is raised by the muscle as a whole, it may be 
carried at the same time forward or backward by the vary- 
ing action of these different fibres. 

There are many of the muscles of the body which are 
thus made to produce various results by variation of the 
action of different parts of the same muscle. And the regu- 
lation of this variation by the nerves is one of the most 
wonderful and mysterious things which we find in our study 
of the nervous system. 

For each fibre, in the cases referred to, is told, as we may 
express it, just how much it must do in order to produce the 
requisite general motion of the muscle. It is manifestly much 
more wonderful thus to produce various but accurately 
graduated contraction in different parts of the muscle, than 
to produce a uniform contraction in all its fibres. 

At i is the biceps muscle, which bends the forearm upon 
the arm, and at c is another muscle that assists the biceps. 
At e is the large muscle in the back of the arm, which acts 



THE MUSCLES. 



»;; 



Fig. 41. 




LE8 OF THE BODY. 



68 PHYSIOLOGY AND HYGIENE. 

in opposition to the biceps, and straightens the forearm upon 
the arm. At d is a muscle which rolls the radius outwards, 
and thus turns the palm of the hand upward as seen in the 
Figure. 

At g is a very large broad muscle coming from the whole 
length of the back. At the axilla or arm-pit, its fibres are 
collected, twisted, and folded upon each other, and it is fastened 
by a stout tendon to the upper and back part of the bone of 
the arm. Its office is to pull the arm backwards and down- 
wards. 

At h is a serrated muscle which, rising from the ribs, goes 
to the shoulder-blade, and serves to draw the shoulder-blade 
forwards. At i is one of the broad muscles of the abdo- 
men. At I and h are two large muscles that move the 
thigh. At o and p, as seen on the right thigh, and at n, as 
seen on the left, are three large muscles, which are fastened 
to the kneepan, and serve to throw the leg forward. 

At q is the tendon that forms the outer hamstring, and 
at r are the two tendons which form the inner one. The 
muscles to which these tendons belong, serve to bend the 
leg upon the thigh, drawing it upward and backward. At s 
is the muscle which makes the bulk of the calf of the leg. 
It moves the heel upward and backward, and it is seen 
in t in the right leg of the Figure. Its strong tendon 
which is attached to the top of the heel-bone is called, on 
account of its strength, the tendon of Achilles. This muscle 
is in Fig. 28 the power P which raises the weight of the 
body, W, on the fulcrum, F, as the heel is raised from the 
ground in walking. 

In Fig. 42 you have a rear view of the muscles. At a is a 
very broad muscle, which, rising from the back, is attached 
to different parts of the shoulder-blade. You can see that 
this irregularly-shaped muscle will move the shoulder-blade 
variously, according to the various action of the different 
fibres of the muscle, which run in so different directions. 

At c 9 you see the rear part of the muscle that raises the 
arm. At b is the extensive muscle that you saw in Fig. 41 
at g, which draws the arm backward. At e is a large muscle 



THE MUSCLES. 



69 



Fig. 42. 




BBAB Y1KW Of rHB MUSCLES. 



70 PHYSIOLOGY A^D HYGIEKE. 

that draws the thigh backward. At g, h, and / are the 
muscles whose tendons form the two hamstrings. At i is 
the muscle that forms the calf of the leg, and raises the heel. 

91. The JBones are not all that the Muscles 
move. — Thus far the bones have been especially spoken 
of as being moved by the muscles. But other parts are 
moved by them also. In the cas3 of the voice, the little 
muscles move cartilages to which the vocal ligaments are 
attached. The tongue and the palate are moved by muscles. 
Muscles move the skin. The mouth, the eyelids, the eye- 
brows, &c, are moved by them. In many animals the skin 
is moved extensively by muscles, as, for example, when the 
horse shakes his skin to get rid of the biting flies. 

92. Symmetry of Arrangement. — The muscles 
moving the fingers are placed mostly in the forearm, while 
their slender tendons pass over the surface of the bones in the 
wrist. The flowing outline of the arm is thus secured, and 
the hand is made a light, and at the same time a strong ap- 
paratus. Substantially the same can be said of the ar- 
rangement of the muscles and tendons in the leg and foot. 

There is a contrivance in a muscle that bends the toes 
which will be noticed here. Its four tendons pass to the 
last bones in the toes, and in doing so they go through the 
tendons of the muscle that bends the second joints. For 
this purpose, the latter divide near the ends where they join 
the bones. In the fingers, also, a similar arrangement is 
made for the tendons of the second and third joints. This 

Fig. 43. 




is represented in Pig. 43, in which e is the tendon which 
goes to the last bone c through the division in/, which goes 
to the second bone i. It is manifest that this is the best 
way of packing the tendons, as we may express it. Any 



THE MUSCLES. U 

other conceivable arrangement would add to the bulk of the 
finger. As they are represented in the figure they are raised 
up, instead of being closely packed down upon the bone, as 
they are in reality. 

93. Modes of Action of the Muscles. — Your atten- 
tion is called to one mode of action, in which a large number 
of the muscles are called into play, on account of its analogy 
to an expedient often used in mechanics. This, represented 
by Fig. 44, is called the toggle-joint. 

Let c, (u and r, b, represent two bars connected together, 
like a carpenter's folding rule, by a hinge or 
joint at c. Suppose the two ends, a and b, to FrG - 4 ^- 

be fitted into the tw r o blocks represented in r— — — 

the Figure. If now the block at b is fixed, ' *\ 

and the block at a is movable, and force be / / 

applied to the joint c carrying it towards d, // 

the block at a will be pressed upward with c(pf- d 

considerable force. If, on the other hand, the V \ 

block at b is movable, and that at a is fixed, \\ 

the block at b will be pressed downward. We r-^ — 

see this latter form of the contrivance applied ^ — ' 

in printing-presses. ^ toggles 

In the human body this toggle-joint is used 
in both ways. When one stoops to take a heavy weight 
upon his back or shoulder, he puts both the knee and the 
hip-joints in the condition of the toggle-joint when it is 
bent; and then as he straightens up, the weight is raised 
by an action of the joints precisely similar to that of the 
toggle-joint in machinery. In the case of the knee, the 
straightening of the joint is done by the muscles on the 
front part of the thigh, that draw up the kneepan with the 
tendon attached to it. 

This is using the principle of the toggle-joint in pressing 
upward. It is also sometimes used in pressing downward. 
In crushing any thing witli the heel, we give grea4 \'<>vr>- to 
the blow on the principle of the toggle-joint, by flexing the 
knee and straight* aing the limb as we bring down the heel 
upon the thing to be crushed. In pushing any thing before us, 



72 PHYSIOLOGY AND HYGIENE. 

we bend the elbow as preparatory to the act, and then thrust 
the arm out straight, thus exemplifying the toggle-joint. 

The horse gives great force to his kick in a similar manner. 
The great power exerted by beasts of draught and burden is 
to be referred mainly to the principle of the toggle-joint. 
When a horse is to draw a heavy load, he bends all his limbs, 
especially the hinder ones, and then as he straightens them, 
he starts the load. In this case the ground is the fixed block 
of the mechanism, the body of the horse to which the load 
is attached is the movable one, and his limbs are so many 
toggle-joints. By this application of the principle we see 
draught-horses move very heavy loads. 

94. The Hand. — The hand is the most wonderful of 
all parts of the body, in regard to variety and complication 
of movement. There are over fifty muscles, which are en- 
gaged in the various motions of the upper extremity, all of 
which, of course, have more or less reference to the hand. 
Indeed the hand is the part of the upper extremity to which 
all its other parts are tributary, and therefore we may 
properly consider all these muscles as in a great measure 
belonging to the hand. 

If now you call to mind the fact, that each one of these 
muscles can vary the amount of its contraction in all degrees, 
from the most powerful action down to the slightest move- 
ment, you can readily see that fifty muscles with this power 
of variation can produce an almost endless number of com- 
binations of motion. The variety would be exceedingly great, 
even if every muscle, whenever it acted, had always the same 
amount of contraction. But the power of varying the 
amount of contraction multiplies the variety to an incon- 
ceivable extent. 

95. The Muscular Sense. — The question arises, 
how in all the diversified action of the muscles their nice 
adjustment is effected. How do the muscles know, as we 
may express it, just how much to do in each movement? 
When, for example, you reach your hand up to touch some 
object, how does each muscle know just what degree of con- 
traction is necessary to make the hand go with precision to 



THE MUSCLES. J '.] 

the particular point arrived at ? And so when one is playing 
on an instrument with the ringers, as the piano, varying 
their pressure continually in accordance with the desired 
loudness of the sound, how does each muscle know just what 
amount of contraction is required of it in each movement ? 
Though the senses of vision and touch afford some assistance 
in the guidance of muscular action in such cases, something 
else is manifestly necessary. 

Sir Charles Bell, therefore, supposes that there is what he 
calls a muscular sense, which acts as a guide to the muscles, 
in connection with the senses of sight and touch. In some 
cas:s it is the sole guide. On this subject, Sir CMiarles says, 
*• When a blind man, or a man with his eyes shut, stands 
upright, neither leaning upon nor touching aught; by what 
means is it that he maintains the erect position ? The sym- 
metry of his body is not the cause; the statue of the finest 
proportion must be soldered to its pedestal, or the wind will 
cast it down. 

u How is it, then, that a man sustains the perpendicular 
posture, or inclines in due degree towards the winds that 
blow upon him ? It is obvious that he has a sense by which 
he knows the inclination of his body, and that he has a 
ready aptitude to adjust it, and to correct any deviation 
from the perpendicular. What sense then is this ? He 
touches nothing, and sees nothing; there is no organ- of 
sense hitherto observed which can serve him, or in any 
degree aid him. Is it not that sense which is exhibited 
so early in the infant, in the fear of falling ? Is it not the 
full development of that property which was early shown in 
the struggle of the infant while it yet lay in the nurse's 
arms ? 

"It can be only by the adjustment of muscles that the 
limbs are stiffened, the body firmly balanced, and kept erect. 
There is no source of knowledge, but a sense of the degree 
of exertion in his muscular frame, by which a man can 
kn >w the position of his body and limbs, while he has no 
point of vision to direct his efforts, or the contact of any 
external body. 
" 4 



74 PHYSIOLOGY AND HYGIENE. 

In truth, we stand by so fine an exercise of this power, 
and the muscles are, from habit, directed with so much pre- 
cision, and with an effort so slight, that we do not know 
how we stand. But if we attempt to walk on a narrow ledge, 
or stand in a situation where we are in danger of falling, or 
rest on one foot, we become then subject to apprehension; 
the actions of the muscles are, as it were, magnified and 
demonstrative of the degree in which they are excited." 



CHAPTER VI. 

LANGUAGE OF THE MUSCLES, 

96. All Thought Expressed by Muscular 
Contractility. — As the nerves of sensation are the inlets 
of all knowledge to the mind, the nerves of motion are the 
outlets by which all knowledge is communicated. Thought 
and feeling are expressed only by muscular motion. 

It is chiefly by the voice that thought and feeling are 
communicated. And every variation of note, or of articu- 
lation, is caused by the action of muscles. When the mus- 
cles of the hand, by writing, communicate to others thought 
and feeling, they merely translate the language of the mus- 
cles of the vocal organs into conventional signs. Leaving 
the language of these vocal muscles for another chapter, in 
this we will notice the language of the other muscles of the 
body and especially of those of the face. 

97. Muscles of Expression in the Face. — 
The particular muscles of expression in the face, are 
represented in Fig. 45. There is a thin flat muscle covering 
the whole top of the head, represented at 1, 2, and 3 ; 3 
being its thin tendinous part. It is fastened to the large 
bones behind, and in front its fibres end in the skin of the 
forehead and the eyebrows, and in the circular muscle of 
the eyelids, 4. When it contracts, therefore, it raises the 



THE LANGUAGE OF THE MUSCLES. 75 

skin of the forehead and the eyebrows ; and if it contract 
strongly, it wrinkles the forehead. The circular muscle of 
the eyelids. 4, when it contracts closes the eye. This and 
the large frontal muscle just described, must have much to 
do with the expression of the countenance. 

Fig. 45. 




MUSCLES OF THE FACE. 

A very important though small muscle, not seen in the 
figure, may be seen at a, in Fig. 32. It is attached to the 
bone at the side of the top of the nose, and is inserted into 
the skin of the eyebrow. It is called the corrugator super- 
cilii, or wrinkler of the eyebrow. From the agency which 
this muscle has in the expression of certain passions and 
emotions, comes the word in so common use, supercilious. 
Though a little muscle, it is truly a supercilious one. 

At 7 is the circular muscle of the mouth, orbicularis oris. 
When this contracts it closes the lips, and if it act strongly 
it pushes them out. This is the muscle with which, in part, 
pouting is done. At 8 is a muscle which IS fastened above 
to the bone of the nose, and runs down, its fibres ending in 



7G PHYSIOLOGY AXD HYGIEKB. 

the wing of the nose, and in the upper lip. When it con- 
tracts, therefore, it moves the wing of the nose outward, 
and draws up the lip. You see this muscle in action in 
some emotions, the nostrils appearing spread out. At 9 is a 
muscle which raises the lip, and at 10 and 11 are two 
muscles, that raise the corner of the mouth, carrying it a 
little to one side. At 13 is the muscle which acts in oppo- 
sition to the two last. It pulls the corner of the mouth 
down. At 12 is the muscle which pulls down the lower lip. 
At 18 is the muscle in the side of the mouth, which draws 
the corner of the mouth backward, and also serves to press 
the cheek inward, and thus prevent the food from getting 
outside of the teeth when we are chewing it. This muscle 
also, by its compressing power, forces out the air from the 
mouth when the cheeks are distended, as in blowing a horn 
or a trumpet. Hence it is called buccinator from buccinare, 
to blow a trumpet. At 15 is a large muscle which closes 
the lower jaw against the upper, and although its chief use 
is to masticate the food, it has some agency in the expression 
of the countenance, in fixing the teeth firmly together, as 
in the expression of rage. There are three muscles which 
move the ear: 19, moving it upward; 17, forward; and 21, 
backward. These have but little power in man, but in some 
animals they move the ear considerably, and are prominent 
agents of expression. 

,98. 31uscles about the 3Iotith.—In Fig. 46 the 
muscles about the mouth, which have so much to do with 
the expression of the countenance, are very distinctly shown. 
At a is the muscle which draws up the wing of the nose and 
the lip ; b raises the lip ; c raises the corner of the mouth ; 
d and e raise the corner of the mouth, and at the same time 
carry it outward ; n draws it outward ; m draws it down- 
ward and outward, in which action it is assisted by a broad 
thin muscle, o, which, situated just under the skin, comes 
up from the neck ; I draws the lower lip downward ; and i 
is the circular muscle which closes the lips, and thrusts 
them out in pouting. At h is a short muscle which is 
fastened to the sockets of the teeth, and has its fibres ending 



THE LANGUAGE OF THE MUSCLES. 

in the skin of the chin. It therefore draws the chin up 
when it contracts. It has so much agency in the expression 
of scorn and contempt that it lias been called the superbus. 
It is by the action of this muscle, together with the circular 

muscle i, that the expression termed pouting is produced. 

Fig. 46. 




I m 

MUSCLES ABOUT THE MOUTH. 

Most of the muscles which have been described are in pairs; 
and in every pair both muscles contract always exactly alike, 
unless affected by disease. We laugh and frown and weep 
on both sides alike. All of these muscles of expression in 
the face are governed in their action by the branches of one 
nerve, the respiratory nerve of the face. When this nerve, 
therefore, is paralyzed on one side, and not on the other, as 
is no uncommon occurrence, these muscles on the paralyzed 
motionless, and the individual can laugh and frown 
and weep on only one side of the fac 
No one muscle is do voted to the ex pre '.-.-ion of one emotion 
don is commonly the result of the com- 
bined action of many muscl rirtue of thia coml 
tion. the Bame muscle often takes a part in the ezprefi 
of various emotions. 



78 PHYSIOLOGY AND HYGIENE. 

99. Action of Particular Muscles in Express- 
ing Emotions.— When the frontal muscle (1, 2, 3, Fig. 45) 
contracts it raises the eyebrows. This motion expresses either 
doubt or surprise, and the observer determines which it is, by 
the expression of other parts of the countenance accompany- 
ing it, or in other words, by the action of other muscles in 
the face. When this muscle contracts very strongly, it draws 
up the eyebrows so much, as to push up the skin of the 
forehead, and wrinkle it. This, as you will soon see, is one 
of the many motions of the face which make up the ex- 
pression of great bodily fear. In joy this muscle acts mod- 
erately ; raising the eyebrow, therefore, but a little. This 
muscle often acts in connection with the corrugator super- 
cilii, the wrinkler of the eyebrow. The muscle which draws 
the corner of the mouth down is in action while the superbus 
(A, Fig. 46,) is drawing up the chin which pushes up the lip 
before it. At the same time the muscle which draws up the 
wing of the nose and the lip (a, Fig. 46,) contracts to some 
extent, producing an arching of the mouth and a peculiar 
shape of the wings of the nose. The upper lip is arched by 
the action of this muscle in such a way as to fit the arching 
upward of the lower lip, produced by the superbus and the 
muscle which draws down the corner of the mouth. 

In the expression just described, and illustrated by the 
figure, it can be seen that the muscle which draws down the 
corner of the mouth has a considerable agency. Now, this 
muscle is the chief agent in the expression of sorrow, as you 
saw in the first part of this chapter. The difference in the 
two cases lies in the combination of action of the muscles. 
Thus, in sorrow the muscle which draws down the corner 
of the mouth, does not have the superbus to act with it, as 
in the case of the passion. So also, in some forms of grief, 
the corrugator supercilii acts quite strongly, where the grief 
is represented as caused by bodily pain. 

In quiet sorrow this muscle is not in action, but there is 
a general languor relaxing the muscles of the face, while 
the corners of the mouth are slightly depressed. It is a 
state of the muscles directly opposite to that which exists 



THE LANGUAGE OF THE MUSCLES. 79 

when there is a calm quiet pleasure. Then most of the 
muscles are in a state of gentle action, and the corners of 
the mouth are a little raised, giving the radiance of a light 
smile to the whole countenance. The frontal muscle 
slightly raising the eyebrows, adds to the effect. 

100. Movements of the Eye in Expression. 
— The muscles of the eye, that is, those which move the 
eyeball, have some agency in certain expressions of the 
countenance. Thus, the fixing of the eye upon an ad- 
mired object makes a part of the expression of admiration. 
In the expression of devotion the eye turns instinctively 
upward. There are certain involuntary motions of the 

all, which have much to do with expression in certain 
states of the body, and in certain emotions. These motions 
are performed by the oblique muscles. When the straight 
muscles which ordinarily control the motions of the eye 
lose their power from a state of general insensibility, the 
eye is given over to the action of these oblique muscles, 
which are involuntary, and therefore is rolled about in its 
socket, being turned upward all the time, so that only the 
white of the eye is seen. This occurs in sleep, in fainting, 
in the stupor of disease, and in the approach of death. 

The loss of power in the voluntary muscles of the eye- 
ball and eyelid is often seen ludicrously exhibited in the 
intoxicated man. He squints and sees double from de- 
ficiency of action in the straight muscles of the eyeball. 
The oblique involuntary muscles of course roll the eye in 
proportion to the deficiency of these straight muscles. The 
voluntary muscle too, which holds up the upper lid, fails to 
do its duty, and the lid is constantly disposed to fall over 
the eye. The frontal muscle is therefore called upon to aid 
it. Hence, in the effort of the drunkard to keep his eyes 
i. you see him raise the eyebrows, the eyelids of course 
being dragged up after them slightly. 

101. Combination of Muscular Action.— But 

we do not get a full view of the combinations of muscular 
action in expression, if we confine our observations to the 
countenance. The muscles of other parte of the body, and 



80 PHYSIOLOGY AND HYGIENE. 

sometimes of the whole frame, are brought into action in 
connection with the muscles of the face, in expressing 
thought and feeling. The attitudes and motions of other 
parts of the body correspond with the attitudes and mo- 
tions of the countenance, so as to produce a harmonious 
effect. The hand is more used than any other part in aid 
of the countenance in expression ; but the whole body is 
often brought more or less into action. The character of a 
passion can sometimes be inferred merely from the atti- 
tude or from the mode of walking, as you see one at a dis- 
tance. 

102. Action of the Respiratory Muscles.— But 
it is the muscles of the respiratory organs which sympathize 
most with the muscles of the face in expression. This 
sympathy is the result of a nervous connection, and the 
nerve of expression in the face is therefore sometimes called 
the respiratory nerve of the face. In laughing the indi- 
vidual draws in a full breath, and then lets it out in short 
interrupted jets, the muscles of the throat, neck and chest, 
especially the diaphragm, being convulsively agitated. And 
if the laughter be strong and continued, he holds his sides, 
which become really sore, from the violent action of the 
respiratory muscles in this expression of his emotions. In 
weeping too, these same muscles are affected. The dia- 
phragm acts spasmodically, the breathing is cut short by 
sobbing, the inspiration is quick, and the expiration is slow, 
and often with a melancholy note. But it is not alone in 
these marked cases that the respiratory muscles are seen to 
act, their action is plainly noticeable in many of the slighter 
expressions of feeling. \ 

103. The Habitual Expression of the Coun- 
tenance after Death. — The lialitual expression of the 
countenance, depending as it does upon the habitual con- 
dition of the muscles, is seen after death. In the state of 
relaxation which occurs immediately at death the face is 
very inexpressive, because its muscles, together with those 
of the whole body, are so entirely relaxed. But very soon they 
begin to contract, and they assume that degree of contrac- 



.. 



81 



tion to which they were habituated during life, and tin - 
_ i to the countenance its habitual ision. 



MUSCLES. 



CHARACTER 

FUNCTION. 

ATTACHMENT. 



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T1I.E. 



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By TEHDONfl to Tin: 



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CHAPTER VII. 
DIGESTION. 

104. Summary of the Process of ingestion* 

— Under the term digestion are included all thoc 
which are necessary to effect the separation from the food 
of its nutritious portion, and the introduction of it into the 
circulation. A summary of these pn nay be thus 

given. The food is broken up and ground in the mouth, 
and it is at the same time mixed with the saliva. I 
then taken into the stomach, where it is kepi in constant 
motion under the sol\. fluid of a peculiar 

character. When it is brought inl ; it ion, it 

1 from the stomach into the in 
acted upon by two fluid- — the bile, tl 
and the a 

bread T. g - • fcioi gency in Be] 

from tli .Jtritiou- u. and I 

or taken up. in the form of a milky fluid, by bul- 
lying on the surface of the inner membrane of the in 



82 PHYSIOLOGY AND HYGIENE. 

tines. These vessels unite to form a large tube, through 
which the milky fluid is poured into the circulation, to 
replenish the blood. 

105. Teeth Various, according to Different 
JKinds of Food. — Mastication is an important part of 
the process of digestion. The teeth, which perform this 
act, are very hard bodies. The body of a tooth is composed 
of two substances. The inner part is called the ivory, and 
the outer, which is exceedingly hard, is called the enamel. 
The teeth are of different shapes for different modes of 
action. There are long and pointed teeth, for tearing; 
others for cutting, which have a sharp edge ; and others 
for grinding, which have for this purpose a broad and 
irregular surface. 

The teeth are differently shaped in different animals, 
according to the kinds of food which they eat. Thus, the 
herbivorous, or vegetable-eating animals, have grinding teeth 
to bruise their food ; while the carnivorous, or flesh-eating 
animals, have sharp-edged teeth,and long-pointed teeth, by 
which their food is torn and cut in pieces. And it is to be 
observed, that the movement of the jaws always corresponds 
to the character of the teeth. 

In the carnivorous animals, the motion of the lower jaw 
upon' the upper is a mere up-and-down, or hinge-like 
motion. As they have no grinding teeth, there is no need 
of any lateral* motion. But in the animals that have grind- 
ing teeth, there is a lateral motion, to enable them to grind. 
You see this difference very plainly, if you observe the dog 
and the horse while they are eating. In Fig. 47 you see 
represented the teeth of a carnivorous animal. The front 
teeth are long and pointed, for rending, while the back 
teeth have a sharp edge for cutting. 

In Fig. 48 you see represented the broad and irregular 
grinding surfaces of the teeth of herbivorous animals. In 
animals that live- on insects, the teeth present conical 
points, which press into corresponding depressions in the 
opposite jaw, as represented in Fig. 49. In those that live 
on soft fruits, the teeth are rounded, as in Fig. 50. These 



DIGESTION. 



8:; 



are quite in contrast with the tearing teeth of the carnivo- 
rous, and the grinding teeth of the herbivorous animals. 



Fig. 47. 




Fig. 48. 




TEETH OF HERBIVOROUS 

Animal. 



TEETH OF CARNIVOROUS ANIMAL. 



There is an arrangement of the enamel and the ivory in 
the teeth of the herbivora which ought not to pass unnoticed. 
Instead of having the enamel cover the ivory, as in the 
teeth of the carnivora, the two substances are arranged in 



Fig. 49. 



Fig. 50. 





TEETH OF FRUGIVOROU9 
ANIMAL. 



TEETH OF INSECTIVOROUS ANIMAL. 



upright layers, as seen in Fig. 48. The object of this is plain. 
The ivory wears away more readily than the harder enamel, 
and, therefore, the surfaces of the teeth always present pro- 
jecting hard ridges, fitting them for grinding thoroughly. 
A miller would say, that these are stones that never need 
picking. 

fOO. Man m> Omnivorous Animal.— So perfect 
is the correspondence of the teeth with the kind of food on 
which the animal liyes, that the skillful naturalist can 
infer very correctly, from the examination of the teeth 



84 



PHYSIOLOGY AND HYGIEXE. 



alone, the character of the food on which an animal lives, 
and even the general arrangement of its structure. 

As man has the three kinds of teeth which I have noticed, 
he is said to be omnivorous, or an eater of all kinds of food. 
In him, the front teeth are the cutting ones ; what are 
called the stomach and eye-teeth are the tearing ones ; and 
the large back teeth are shaped for grinding. It will be 
observed that the tearing teeth, as they have not very sharp 
points and are no longer than the other teeth, have but 
little power when compared Avith the long and sharp tearing 
teeth of a carnivorous animal, as seen in Fig. 47. As man 
can use instruments to cut his food in pieces, he does not 
need so much power in his teeth as carnivorous animals 
have. Allowance should be made for this in estimating 
the amount of carnivorous adaptation in man. 

107. Substitutes for Teeth. — There are a few of 
the Mammalia that have no teeth. This is the case with 
the common whale. In his case, instead of teeth, there 
hang down from the upper jaw, as represented in Fig. 51, 

Fig. 52. Fig. 51. 




WHALEBONE. 



SKULL OF WHALE. 



plates of a fibrous substance, called whalebone, which have 
their fibres separated at their free extremities, so as to make 
a sort of sieve. This is intended to catch the small ani- 
mals, which the whale devours in great numbers. 

To obtain these it swims with its mouth opened and thus 
fills it with water. The water is strained through the 



DIGESTION. 



85 



fibrous whalebone, and the small animals retained. Birds, 
too, have no teeth. Their place is supplied in part by a 
contrivance in the stomach itself, for the breaking up of the! 
food. This will he described in another part of this chapter. 
10$. Salivary (Hands. — While the food is cut and 
ground by the teeth, it is at the same time thoroughly 
moistened by the saliva, which is poured forth from certain 
glands in the neighborhood. There are thre i pairs of these 
glands. Fig. 58 shows the glands on one side. The parotid 

Fig. 53. 




SALIVARY GLANDS. 



gland, 1, is the largest. This is situated in front of the 
lower part of the ear. It is the seat of the swelling in the 
disease called mumps. Its duct, 2, passes over one large 
muscle and between the fibres of another, and pours its 
contents into the mouth opposite the second small grinder 
of the upper jaw. If you press on this part of the cheek, 
yon can feel in the mouth an increased flow of the saliva. 

The submaxillary gland, 3 3 is situated inside the lower 
jaw at its lower part: and its duet. 4, opens into the 
mouth at the side of the fraenum of the tongue. The sub- 
lingual gland, 5, lies under the tongue, and discharges it- 
secretion by ducts at the side of that organ. 



86 PHYSIOLOGY AND.HYGIEXE. 

109. Action of the Salivary Glands. — These 
glands are especially active when we are eating ; and it is com- 
monly estimated that, during an ordinary meal, about eight 
ounces of saliva are poured into the mouth. This large 
amount is wanted to moisten the food thoroughly before it is 
swallowed ; and it also has some chemical influence in pre- 
paring the food for the action of the gastric juice in the 
stomach. More saliva than usual is needed, also, when we are 
speaking, in order to keep the parts properly lubricated, for 
the passage of the air in and out during speaking dries up 
the saliva by evaporation. And, accordingly, the motion of 
the parts at such times stimulates a larger flow, just as pres- 
sure on the cheek will do it, as before remarked. This result 
is favored by the course of the duct of the parotid gland, 
which, as you have seen, passes over one large muscle, and 
then through the body of another. 

Chewing excites an increased flow of the saliva ; and the 
tobacco chewer does a real injury to the salivary glands, by 
keeping them constantly in excessive operation, to say 
nothing of the ruinous effects of this drug on the system at 
large. 

110. Flow of Saliva affected by Sympathy. 
— It is supposed that, besides the mere mechanical stimulus 
of the motion of the parts, the stimulus of sympathy is also 
concerned in exciting these glands to increased action. The 
glands are supposed to be affected in this way by the stimu- 
lation of the food on the surface of the mouth, about the 
orifices of their ducts. That sympathy does have an influence 
on their secretion is evident from the very familiar fact, 
that the thought of food will often, as it is expressed, cause 
the mouth to water. 

111. Difference in the Character of the 
Scdiva. — The fact that these glands do not all secrete the 
same kind of fluid, has led to an interesting discovery in 
relation to them. The submaxillary glands secrete a viscid 
fluid, while that which is poured forth by the parotid and 
sublingual glands is perfectly limpid. Now it has been 
found, by various observations and experiments on animals, 



DIGESTION. 87 

that while the teeth are cutting and grinding the food, and 
the parotid and sublingual glands are pouring out the saliva 
to moisten it, no secretion conies from the submaxillary 
glands. 

But these glands pour out their viscid fluid the moment 
that the tongue thrusts the food back towards the throat, 
in the beginning of the act of swallowing. The special ob- 
of this viscid fluid is then to cover the food, so that it 
may, to use a common expression, slip down easily into 
the stomach ; and it has nothing to do with the moistening 
of the food, this being the particular office of the other two 
pairs of glands. 

112. Swallowing. — When the food has been ground 
by the teeth, and moistened by the saliva, it is carried by 
the act of swallowing into the stomach. This act, simple 
as it may appear to you, is a very complicated one, and is 
performed by the conjoined and agreeing action of many 
different muscle-. The food is first thrust back over the 
surface of the tongue into the large cavity in the back of 
the throat, called the pharynx. Into the pharynx two 
tubes open — the ccsophagus or gullet, which is the passage 
into the stomach, and the trachea* or windpipe, the passage 
to the lungs. 

As the oesophagus lies behind the trachea, the food, in 
passing to it, must go directly over the opening into the 
trachea. To prevent the food from entering the trachea, 
therefore, there is a little tongue-shaped body, called the 
lottis, extending back from the root of the tongue, and 
acting as a lid to the glottis, the opening into the trachea. 

When we are swallowing, this lid is shut down ; but it is 

always raised up when we are breathing or speaking. When 

-wallow, not only does the lid shut down, but the larynx 

meet the lid, as you may readily perceive, if you 

- your fingers upon what is called Adam's apple while 

* Tli is term is Bometimea used, as here, to mean the whole of the 
tube conducting to the lungB, includi] jrox, which is at the top 

of this tube, and Bometimea it is restricted to that 
which is below the larynx. 



88 PHYSIOLOGY AND HYGIENE. 

you are swallowing. In Fig. 54, you have a side view of the 
parts engaged in swallowing, as if the head were divided 
into two halves by a vertical section. At i, is the cavity of 
the nostril ; at h, are the lips ; a is the divided bone of the 
chin ; b is the tongue, between which and the spinal column, 
is /, the large cavity of the pharynx. In front of this cavity 
hangs the palate, g, as a door or valve, to direct the air com- 
ing from the trachea, d, either through the mouth or through 

Fig. 54. 




VERTICAL SECTION OF THE THROAT. 



the nostrils, according to its position. The oesophagus, e, is 
behind the trachea, and the epiglottis, c, shuts down when we 
swallow, to let the food pass over it into the oesophagus. In 
Fig. 55, you have a view of the same parts from the rear. 
At 1, is a section of the bones at the base of the skull ; 3, 3, 
are the cavities of the nostrils ; 2, 2, the walls of the pharynx 
spread apart ; 5, the pendulous palate ; 6, 6, the arch of the 
palate ; 8, the root of the tongue ; 9, the epiglottis, and 10, the 
glottis, or opening into the larynx ; 13, the oesophagus ; 14, 
the trachea. The pharynx, you see, is a funnel-shaped 
cavity, tapering down to the oesophagus, the opening of 
which is considerably below the opening of the trachea. 



DIGESTION. 



89 




VIEW OF THE THROAT FROM 

BEniND. 



113. Action of the (Eso- Fig. 55. 

phagus. — When the food en- 
ters the oesophagus, it is carried 
through that tube into the stom- 
ach by the action of muscular 
fibres. These fibres are represented 
in Fig. b6. The circular fibres are 
seen at a and b. These are re- 
moved at c, so as to show the 
longitudinal fibres. It is by the 
consent of action between these 
different sets of fibres that the 
food is propelled through the 
oesophagus. 

As the food descends, a dilata- 
tion of the circular fibres must 
everywhere take place where the 
food is, and a contraction of them 
immediately behind it — the dilatation mak- 
ing the way for it, and the contraction forc- 
ing it along. And in animals that chew the 
cud, these actions force the food from the 
stomach into the mouth. 

114. Hie Gastric Juice. — The food 
being introduced into the stomach, is here 
subjected to the action of the gastric juice. 
This is a peculiar fluid, somewhat acid in 
its character, which is secreted by very min- 
ute follicles, or bag-like cavities, situated in 
the substance of the mucous membrane. 
Ordinarily there is none of this fluid in the 

lach when no food is there. Dr. Beau- 
mont m interesting observa- 
i this, as well as many oilier points, 
in the remarkab which fell under his 
care. 11 da St Martin, had 
received a wound in his left side by 
bursting of a gun. The wound, which 





TCAGT78 



90 PHYSIOLOGY AND HYGIENE. 

opened into the stomach, never entirely closed, but an 
orifice remained, through which Dr. Beaumont could look 
into, and observe what was going on in the stomach. 

He describes the mucous membrane, in its healthy state, 
as having a velvet-like appearance, with a pale pink color, 
and as being covered with a very thin, transparent, viscid 
mucus. On introducing some food, or irritating the mucous 
membrane mechanically, he saw, by the aid of a magnify- 
ing glass, "innumerable lucid points" projecting on the 
surface, and from these exuded a pure, limpid, colorless 
fluid. These points were the follicles which secrete the 
gastric juice, rendered turgescent by being stimulated to 
action. 

115. Quantity of Gastric Juice. — The amount 
■ of gastric juice secreted is generally about in proportion to 

the amount of food which the necessities of the system re- 
quire. When the quantity of food taken is very much 
more than is required, there can not be a sufficient amount 
of gastric juice secreted to digest all of it ; and some 
must therefore remain undigested, and will prove a source 
of irritation to the stomach. If the amount of food taken 
from day to day is not very excessive, but is only a 
little above the proper quantity, there will be enough 
gastric juice made to digest it; but the daily overtaxing 
of the powers of the secreting follicles will, after a while, 
produce derangement of the stomach, and perhaps perma- 
nent disease. 

116. Function of the Gastric Juice.— The ac- 
tion of the gastric juice upon the food is of a chemical 
nature. In order that it may act effectually on all portions 
of the contents of the stomach, this organ is kept in con- 
stant motion by the fibres of its muscular coat. These 
fibres are so arranged that, as they contract and relax, they 
keep up a sort of churning of the contents, and thus effect 
a thorough mixture of them with the gastric juice. In 
Fig. 57, you see these fibres represented. At 1, is the open- 
ing of the oesophagus into the stomach ; and at 4, is the part 
which opens into the intestine. The fibres are in different 



DIGESTION. 91 



la vers, running in different directions. The outer peritoneal 
coat, 5, 5, is dissected off and turned back, showing some of 



Fig. 57. 




MUSCULAR FIBRES OF THE STOMACII. 

the fibres that run lengthwise of the organ, G ; and some 
that run crosswise,?; and others, 8, that run obliquely. 
You can readily see what effect the contraction of these 
different fibres will have on the shape of the stomach. The 
contraction of the longitudinal fibres, 6, brings the large, 
bulging end of the stomach, 2, and the small end, 3, nearer 
'her. The transverse fibres, when they contract, di- 
minish the capacity of the stomach transversely. And the 
oblique fibres modify these two motions by their oblique 
action. 

117. Action of the Pylorus— By the combined 

nical and mechanical action of the stomach, its contents 

are, after a little time — in three or four hours — reduced to 

a uniform greyish, semi-fluid mass, called chyme. While 

has been iroing on, the communication beta 
the stomach and the intestines has been entirely closed by 
a valve, called the pylorus. This is represented at 5, in 
58, which | a view of the inside of the stomach. 

This valve is made of a fold of both the mucoufl and the 
muscular coats of the stomach. It is a very faithful sen- 



\>Z PHYSIOLOGY AND HYGIENE. 

tinel, as is indicated by its name, which is derived from two 
Greek words, signifying to guard the gate. It will not 
ordinarily permit any undigested food to pass it. 

While the process of digestion is going on, the motions 
produced by the muscular fibres cause the contents to move 
about, and of course they are thrown against the pylorus, 
as well as any other part of the stomach. But the valve 
remains closed, until some portion comes against it that is 
thoroughly changed to chyme, and is therefore fit to pass 
on into the intestine. It opens to let this pass. 




INTERIOK OF THE STOMACH AND SMAIiL INTESTINE. 

Toward the conclusion of the digestion of a meal, small 
quantities pass at first, and after a while, the contents pass 
quite rapidly through the valve. 

Although this sen tin el- valve thus performs its duty so 
faithfully in relation to nutritive substances, it seems to let 
other substances pass very readily. Solid substances, swal- 
lowed by mistake, as buttons, pieces of money, the pits and 
skins of various fruits, often pass the valve without any 
trouble. The valve seems to be on duty as a sentinel only 
during the process of digestion ; and, if the attempt to go 
through with this process prove unavailing, the pylorus, 



DIGESTIOX. 03 

though it let such hard substances as have been mentioned 
pass without difficulty, resists the passage of the undigested 
food, sometimes causing much uneasiness, and even perhaps 
pam. by so doing. In such a case, either the valve after a 
ume gives over its resistance, or, holding out, the action of 
the stomach is reversed, and the offending matter is thrown 
off by vomiting. 

IIS. Bad Habits in Eating. — The process of 
digestion, as it has been described, is a regular process, re- 
quiring a certain average period of time for its completion. 
If, during the progress of it, fresh food be introduced, its 
regularity is broken in upon, and the process stops. Then, 
too. if. immediately after the completion of the process, a 
new supply of food be taken, harm is done, because the organ 
has not its needed interval of rest. For these reasons, the 
practice of eating between meals is a very injurious one. 

Eating fast does harm, because, — 1st, the food is not 
sufficiently ground ; 2d, it is not mixed thoroughly with 
the saliva ; and, 3d, more food is taken than would be suffi- 
cient to satisfy the hunger if the individual ate slowly, and, 
therefore, more than can be easily digested. Great variety 
in food stimulates the appetite unduly, and too much is 
consequently eaten. Moderate exercise, if it be not violent, 
facilitates digestion. An experiment was once tried upon 
two dogs, which was thought to prove that exercise hinders 
digestion. 

Two dogs were fed freely, and while one was left to lie 
still, the other was made to run about violently. Both dogs 
were killed after an hour or two, and it was found that, 
while digestion had gone on thoroughly in the dog that was 
allowed to remain quiet, in the other the food was undi- 
gested. This only proved that violent exercise, taken im- 
mediately after eating, impedes digestion. It has been 
found, on the other hand, that 1 i _rli t exercise promotes the 
process; and daily experience, among laborers, shows, that 

does not interfere with it, if a 
little interval of rest be allowed, so that the process may be 
fairly begun. 



94 PHYSIOLOGY AND HYGIEXE. 

119. Cause of Hunger. — The sensation of hunger 
has been attributed to various causes, — as the empty state 
of the stomach, the presence of the gastric juice irritating 
the mucous membrane, &c. It cannot arise from empti- 
ness ; for, if so, it should occur sooner than it does after 
eating, and should not be absent in disease, as it often is 
for a long time, when the stomach is almost entirely empty. 
It can not arise from irritation by the gastric juice; for 
it was found by Dr. Beaumont, in his observations of the 
stomach of Alexis St. Martin, that this fluid is not secreted 
till after food is introduced into the stomach. The cause 
of hunger is evidently in the state of the system. It is a 
state of want. 

Nutriment is needed by the formative vessels, the builders 
and repairers of the system, which make their wants known 
as distinctly as the bricklayer does, when he calls for more 
brick and mortar. Through the nerves, an impression is 
communicated to the stomach, and the sensation of hunger 
is the result. 

That the sensation results from impressions made upon 
tke nerves of the stomach is evident from the fact that it 
can be temporarily relieved by putting indigestible sub- 
stances into the stomach. These produce the effect by 
causing other sensations, which take the place, for the time 
being, of the sensation of hunger. After, however, the mo- 
mentary effect is over, the sensation of hunger returns in 
its full force. The cause, then, of the sensation is in the 
system at large, but its seat seems to be in the stomach. 

If disease has impoverished the system, so soon as the 
stomach is in a condition to respond to the call of the for- 
mative vessels that set themselves at work to repair the 
waste, the hunger is often excessive. In order to have the 
sensation of hunger, not only must there be a want in the 
system at large, but the stomach must be in a state fitted to 
receive the notice of this want. And fortunately it is seldom 
in this state except when in a condition to do its work. If 
it were otherwise, food would often be introduced when it 
could not be digested. 



DIGESTION. 95 

1:20. Sensations of Hunger Affected by the 

Mitld. — Mental impressions sometimes incapacitate the 
brain for receiving the notice of the want of the system. 
In this case, the mental impression in the brain counteracts 
the impression conveyed from the stomach, and so neu- 
tralizes the sensation of hunger. Thus, grief often destroys 
the appetite for food. 

121. Thirst* — Nearly the same remarks can be made 
in relation to thirst, that have been made in regard to hunger. 
This sensation seems to have its seat in the fauces or throat. 
Its cause is evidently not there ; for the mouth and throat 
may be very dry, and yet there may be little or no thirst; 
while, on the other hand, there maybe much thirst, although 
the mouth and throat are moist. The cause of the sensa- 
tion is. like the cause of hunger, in the system at large ; and, 
therefore, no local cause, producing a dryness of the throat, 
can cause thirst independent of a general condition. 

122. Arrangement of the Organs of Diges- 
tion. — Fig. 59 exhibits the organs of digestion as they pre- 
sent themselves in a front view, except that they are somewhat 
separated from each other, instead of being as closely packed, 
as they are in the abdomen. The large end of the stomach 
lies to the left side,* and at this end is the spleen. The pan- 
creas is behind the right end of the stomach. Above the 
stomach, and mostly to the right side, is the largest organ 
in the abdomen, the liver. In the Figure, it is represented 
as turned upward. The stomach is directly connected with 
the small intestines at the pylorus. At the end of this long 
and winding tract begin the large intestines. The duct of 
the gall bladder, and that of the pancreas, open into the 
small intestine at its beginning. 

The office of the spleen has not yet been ascertained. 
her has that of the worm-like appendage at the begin- 
ning of the large intestines. The omentum, or caul, which 
hangs like a curtain from the front part of the stomach down 
in front of the intestines, is not represented in the Figure. 

* As this is a front view, the right side of the Figure is the left side 
of the body. 



96 



PHYSIOLOGY AXD HYGIENE. 



123. The Mesentery. — There is one arrangement in 
the abdomen which must not pass unnoticed. If the intes- 



Fig. 59. 



GALL BLADDER 



LARGE INTES- 
TINES. 



BEGINNING OF 
LARGE INTES- 
TINES. 

WORM-LIKE AP- 
PENDAGE. 




SMALL INTESTINES. 

DIGESTIVE ORGANS. 



tines were left to lie loose in this cavity, they would con- 
stantly be subject to displacement and injury. They are 
therefore fastened to the backbone by an arrangement 
which secures them from any such accident, and at the same 
time allows of a sufficiently free motion of different parts 
of this tube. It is this. The intestinal tube makes the 
margin of a broad sheet of membrane, the other edge of 
which is gathered up and fastened to the spinal column, 



DIGESTION. 



97 



Fig. 60. 




PLAN OF THE MESENTERY. 



The device is like a ruffle with a puffed edging. The mem- 
branous sheet is called the mesentery. As the intestinal 
tube, the puffed edging, is much longer than the ruffle 
itself, the mesentery, it is gathered on to the ruffle, as a 
seamstress would express it. Now, the mesentery is com- 
posed of two folds of the peritoneum, the smooth, shining, 
outer covering of the intestines. 

The arrangement will be easily understood by the diagram 
in Fig. 60, which represents a section of the intestine with 
the mesentery. The cavity of 
the intestine, a, is lined by the 
mucous membrane represented 
by the inner circle. Next comes 
the muscular coat, and next the 
peritoneal, the outer, which, in- 
stead of making a circular tube, 
as the other two coats do, passes 
backward on both sides of the 
intestine, to make the mesentery, 
b. After being attached to the 
spine by means of cellular tissue, it is reflected off to pass 
over other portions of the intestine, as seen at c, c. 

Between the two layers of the peritoneal membrane, in 
the mesentery, is considerable space, as seen at b. This 
-pace is filled up with blood-vessels, nerves, and lacteals with 
their small glands, soon to be described, all bound together 
by the common packing material of the body, the cellular 
tissue. You see, therefore, that the mesentery subserves 
more than one use. Besides fastening the whole tract of 
the intestinal canal to the spine, so as to guard it against 
accident, it acts as a secure medium for the passage of 
the blood-vessels and nerves to the intestines. And, be- 
-. it contains the little tubes which convey all the 
nutriment into the blood for the growth and repair of the 
body. 

124. Chyme, Chyle*— The chyme, as it passes into 
the small intestine from the stomach, has mingled with it 
the bile and the secretion of the pancreas. These are poured 



08 



PHYSIOLOGY AND HYGIENE. 



into the intestine at the point represented at 6, in Fig. 58. 
These secretions undoubtedly have some agency in separating 
the nutritious part of the chyme which is afterwards ab- 
sorbed by the innumerable small vessels, called lacteals, 
situated in the mucous membrane. This nutritious part 
of the chyme is a milky fluid, called the chyle. The lacteals 
which absorb it are little tubes or ducts. These enter 
certain glands, called the mesenteric glands, and then pass 
on, as seen in Fig. 61, to pour their contents into the 
thoracic duct. 

Fig. 61. 




OKIGIN 

OP 

LACTEALS. 



SECTION OF INTESTINE SHOWING THE LACTEALS. 



125. Thoracic Duct .— This duct, which is about the 
size of a common quill, running up on the left side of the 



DIGESTION. 99 

aorta, the great artery of the heart, pours its contents into 
the junction of two veins at the top of the chest. Thg 
mode of the joining of this duct with these veins is calcu- 
lated to facilitate the discharge of the chyle. As the two 
large currents in the veins, v and v, in Fig. G2, unite, 

Fig. 62. 




JUNCTION OF THE THOKACIC DUCT WITH THE VEINS. 

there is created, by the forward motion of these currents, 
a tendency to a vacuum at the angle at which they meet, 
the point where the thoracic duct, T, D, opens. There 
is, therefore, a suction power, as it is termed, exerted upon 
the fluid in this duct. The chyle, thus mingling with the 
blood, becomes a part of it. 

1:26. Digestive Apparatus in Different Ani- 
mals* — The digestive apparatus varies much in different 
animals, according to the kinds of food on which they live. 
Afi a general rule, the more the food diners in character 
from the animal itself, the more complicated and extensive 
is the apparatus. Thus, the herbivorous animals have a 
very long alimentary canal, and the beginning of it, the 
stomach, is a complicated organ. While, on the other hand, 
in the carnivora, the flesh Which they eat being very much 
like their own flesh, and, therefore, not requiring a very com- 
plex process of assimilation, the stomach is a simple organ, 
and the alimentary canal is very short. In the Bheep, for 
example, the alimentary canal is about twenty-eight times 



100 PHYSIOLOGY AND HYGIENE. 

the length of the body, but that of the lion only three times 
his length. In man, who lives on a mixed diet, the alimentary 
canal is about six times the length of the body. 

127 • Digestion in the Sheep. — The stomach is 
more complicated in animals that chew the cud than in 
any others. It has four distinct cavities, and a singular 
mechanism is called into operation in managing the food as 
it passes through them. In Fig. 63, you have a representa- 
tion of the stomachs of the sheep, as they appear exteriorly. 
As the animal craps the food, it passes into the first stomach, 
which is little else than a great reservoir to hold and soak 
it. Then it passes into the second stomach, from which it is 
returned into the mouth. On being swallowed again, it passes 
from the (esophagus into the third, and thence into the 
fourth stomach. In Fig. 64, you see the interior of these four 
stomachs ; and by the aid of this illustration I will describe 
the process of digestion in the sheep more particularly. You 
see the very large first stomach, or paunch, in which the 
food is accumulated. It is not yet masticated thoroughly, 
for the animal has swallowed it as fast as he could, and 
packed it away in this reservoir. From this it is passed, in 
small quantities at a time, into the second stomach, the 
honeycomb, so called from the peculiar network of folds in 
it. Here the food is rolled up into balls by the action of the 
muscular fibres in this network. Each ball of food is passed 
up through the oesophagus into the mouth, where it is 
chewed and thoroughly mixed with the saliva. 

Then it is swallowed, and, as it passes from the oesopha- 
gus, instead of going into the paunch, as it did when swal- 
lowed the first time, it is directed through the groove seen 
in the Figure into the third stomach, the manyplies. This 
has many folds, like the leaves of a book, so that the food is 
exposed to a large surface in this cavity. It passes from this 
to the fourth stomach, the reed. Here, and here only, it is 
acted upon by the gastric juice. This, therefore, is the true 
stomach, all the other cavities furnishing only preparatory 
steps to the true process of digestion. It is from this fourth 
stomach that what is called the rennet is taken. 



DIGE^TIOS. 



101 



When fluid matter is swallowed, it goes directly into 
the second stomach, and not into the first, the paunch ; so 
that, in the case of the sheep, the drink goes one way anil 



Fro. 63. 



(ESOPHAGUS. 



ORIFICE OF 

.-TOMACU. 



3d stomach. 




STOMACHS OF THE SHEEP. 



Fig. 64. 



CESOPHAGU? 



MANTPLIE 




interior of 'I in. 9TOMA< H8 OF Tin. 8HFJ r 



102 PHYSIOLOGY AND HYGIENE. 

the solid food another. And, what is still more singular, 
while the animal is a suckling, the milk passes into the 
fourth stomach through only the third, which has its folds 
so closed together as to form a mere tube to conduct it to its 
destination. And the great paunch and the honeycomb 
are wholly useless until the animal begins to crop its food 
for itself. 

128. Digestive Apparatus in Birds. — In birds, 
the digestive apparatus is necessarily yery peculiar, from the 
fact that they do not masticate their food. They have, on 
this account, an arrangement in the stomach itself for 
grinding the food. In the cavity called the gizzard are two 
opposing surfaces, made very hard, so that by rubbing 
together they bruise the grains ; and while the food is thus 
ground, as between two millstones, the gastric juice is 
poured down upon it from above. This arrangement is 
seen in Fig. 65, which represents the digestive apparatus in 
the turkey laid open. 

At b is the gizzard, showing the two hard surfaces, which 
are rubbed together by the stout muscles that make the 
great bulk of the organ. Above, at a, are the glands which 
pour forth the gastric juice. And above this part of the 
stomach there is, in all grain-eating birds, a large sac bulg- 
ing out from the oesophagus, called the crop, which is a 
reservoir for the food, just as the paunch is in the rumina- 
ting animals. In those birds that live on flesh or fish there 
is no such grinding apparatus. The walls of the stomach 
are quite thin, and it presents no hard surfaces. 

The kind of food, the mode of life, and the purpose 
which the animal is designed to fulfill, are the circum- 
stances which govern the variations of the digestive appa- 
ratus. The proportion which the digestive apparatus bears 
to other parts varies very much; and in some of the 
lower orders of animals, the body seems to be all stomach. 
In such cases, the only appendages are those which seize 
the food and direct it into the orifice of this organ. This 
is the case with the hydra, represented in Fig. 1. And, 
what is very singular, the outside of the body of this animal 



DIGESTION. 



103 



is just as capable of acting as a stomach as its inside. For 
when the creature is turned inside out, it will go on catch- 
ing and digesting its food as usual 

Fig. 65. 




I to II OF THE TURKEY. 

But wide as the variations are in the digestive appa- 
ratus of animals, the same object is aimed at in all — the 
□dilation of nutrient substances to the animal, to pro- 
a material from which its structure can be built and 
kept in repair. There is, therefore, much that is common 
to them all in the mode- in which this object ii accom- 
plished. And even the analogy which exists between the 



104 PHYSIOLOGY AND HYGIENE. 

animal and plant, in regard to assimilation, does not relate 
to the fact alone, but in some measure to the modes in 
which the process is effected. 

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CHAPTER VIII. 

CIRCULATION OF THE BLOOD. 

129. Apparatus of the Circulation. —In the 

last chapter was described the manner in which the blood 
is made from the food. The blood, thus prepared, is circu- 
lated in every part of the body, that it may be used for the 
purposes of construction and repair. The apparatus by 
which this is done acts, as we have seen, as the common 
carrier of the material wdiich is used everywhere in the 
body by the laborers, the builders, to whom it is thus 
brought. 

This apparatus consists of several parts — a great central 
organ, the heart ; the arteries, the tubes by which the blood 
is conducted to all parts of the body ; the veins, other 
tubes, which bring the blood back to the heart ; and the 
capillaries, a network of exceedingly minute vessels, through 
which the blood passes as it goes from the terminations of 
the arteries into the beginnings of the veins. 

The blood goes from the heart through a large artery, 
called the aorta, which sends forth branches; and these 
divide and subdivide, so that the extreme arteries, through 
which the blood flows into the capillary network, are very 
minute. And the veins which receive the blood from this 
network to carry it back to the heart, are equally minute ; 
but joining together, as they proceed toward the heart, 
they are at length all united into two great venous trunks, 
one from above and the other from below, which pour 
their contents into this organ. 

The capillaries, taking their name from the Latin word 
lldy a hair, are so small that they can not be Been 
by the naked eve. In any small cut, the blood which <•< 
out comes from multitudes of these vessels, They B 
hold the blood, while the formative cell.-, that construct 



106 PHYSIOLOGY AND HYGIENE. 

and repair the body, may select such materials as they need 
for their purposes. 

130. The Heart. — The heart is a great central forc- 
ing and suction pump, in the midst of this circulating ap- 
paratus. When it contracts, it forces the blood out through 
the aorta and its branching arteries into all parts of the 
system. And when it enlarges or dilates itself, it, by suc- 
tion, as it is termed, fills itself with the blood returning from 
the system through the veins. 

131. The Arteries. — The arteries differ from the 
veins in their structure and arrangement. The arteries are 
firm though elastic tubes, while the veins are lax in their 
structure. The object of the difference is obvious. As the 
blood is forced into the arteries by the powerful action of 
the heart, it is necessary that they should be strong and 
firm. 

When a dilatation does occur in an artery, it is called an 
aneurism. But the arteries need to be firm, not only for 
the sake of security against rupture, but also that the force 
of the heart may propel the blood to the extremities of the 
arterial system. If the arteries were lax tubes, like the 
veins, the impulse would soon be lost in the yielding tubes, 
and the blood would move very sluggishly in the small 
arteries at a distance from the heart. 

What we call the pulse, is caused by this impulse. If the 
arteries were lax tubes, the pulse would not be felt at any 
great distance from the heart. Instead of being distinct, 
as it now is, with every beat of the heart almost to the very 
extremities of the arterial system, it would be rendered con- 
fused by the yielding of the tubes, even quite near the heart, 
and at a distance from that organ it would be entirely lost. 

Besides the firmness of the arteries, there is another cir- 
cumstance which favors the free flow of blood through 
them. It is their mode of division. The branch of an 
artery leaves the main trunk at a sharp angle, making thus 
only a slight deviation from the direction of the main cur- 
rent; while, on the other hand, in the veins where the cur- 
rent flows in an opposite direction, the branch unites with 



THE CIRCULATION". 



107 



the trunk at nearly a right angle. This difference is repre- 
sented in Fig. 66 ; 1 being the artery, and 2 the vein. 

Fig. 66. 

1 2 




ARTERY AND VEIN, 



132. The Veins. — The venous system has a much 
greater capacity than the arterial. That is, all the veins of 
the body are together capable of holding more blood than 
all the arteries are. And the blood moves very rapidly and 
directly from the heart through the arteries, but comes 
back to the heart quite slowly through the veins. Every 
thing is arranged to promote this rapid circulation through 
the arteries, while the venous system is calculated for a slow 
but sure progress of the blood back to the heart. 

To secure this, valves, made of folds of the inner lining 
of the veins, are so arranged as to prevent the blood from 
flowing in the wrong direction. Fig. 67 represents a vein 
cut open bo as to show these valves. A shows the valvt 
they appear when the vein La laid open and spread oul : P>. 
as they appear when the vein is simply laid open; and C 
represents the appearance of the outside of the vein where 
there are valve.-. The need which there is of this hel] 
the circulation through the veinsis obvious. The suction 
power of the heart is not competent, unaided, to move the 



108 



PHYSIOLOGY AKD HYGIENE. 



blood throughout all the lax venous system. These pocket- 
like valves, therefore, are made in the veins to assist the 
circulation there. 

Fig. 67. 

A BC 





VALVES IN THJJ VEINS. 

Every movement of the muscles or other parts about the 
veins tends to keep the blood in motion, and the valves 
serve to prevent this motion from taking the wrong di- 
rection. The difference in force and velocity with which 
the blood moves in the arteries and in the veins, is made 
manifest when they are wounded. The blood flows from a 
wounded vein in a slow and steady stream. From an artery 
it flows rapidly, showing the impulse of the heart in its jets, 
which correspond exactly with the pulse. Hence comes the 
danger in wounding an artery, while the wound of a vein is 
ordinarily attended with no danger. 

133. Protection to the Arteries. — Accordingly, 
we find the arteries so placed, that they can not easily be 
wounded, while many of the veins are quite freely exposed. 

The arteries are deeply seated, except in some few cases 
where this is impossible ; but the veins are often super- 
ficially situated. You can see this, for example, in the bend 
of the arm. Some large veins appear there just under the 
skin, while the artery which supplies the arm is embedded 
among the muscles and tendons. In every part of the body, 
the most secure spot is chosen for an artery. Thus, at the 
knee-joint, the artery, instead % of running over the surface 



THE CIRCULATION. 109 

of bone, where it would be liable to be wounded, lies deep 
in the ham at the rear of the joint. The same is true of 
the elbow-joint, just alluded to, and of other parts of the 
body. Although there are arteries everywhere, they are uni- 
formly so deeply seated, that it is only in a few localities 
that you can readily find one. You can feel one pulsating at 
the wrist, and another on the temple. 

134. Mode of Stopping a Bleeding Artery. — 
It will be proper here to give some practical instruction, 
in regard to stopping the flow of blood from a wounded 
artery; as many lives have been lost from the ignorance of 
bystanders when such accidents have happened. Envelop- 
ing the part in cloths, which is so commonly done at such 
times, does no good, but only serves to catch and conceal 
the blood as it flows. 

Pressure upon the artery, on that side of the wound 
which is toward the heart, will of course interrupt the supply 
of blood from this organ to the wound. Firm pressure with 
the thumb will do it. But the pressure must be made at the 
right point, that is, directly upon the artery. You may not, 
in all cases, press upon the right spot at once. If you do 
not, the blood will continue to flow. In this case press at 
different points, until you find the point at which you see 
that pressure stops the flow of blood from the wound. But 
you may not be able to find the right spot. If you can not, 
you can tie a slip of strong cloth or a handkerchief around 
the limb above the wound, and twist a stick in it until the 
bleeding stops. In one or the other of these ways, you can 
prevent the loss of blood until the surgeon arrives to take 
charge of the cat 

135* Communication between Arteries. — Al- 
though there is no such free communication between 
arte etween the capillaries, there is some 

amount of communication, and particularly in certain parts 
of the body. Audit is well that it is so. for it Bometimea 
helps the surgeon to save a limb, when he could not do it 
if there were no communication. 

An artery has three coats, one of which is a strong fibroufl 



110 PHYSIOLOGY AND HYGIENE. 

one. When this is thinned or ruptured, the other two coats 
bulge out, forming a pulsating tumor. And, as the blood 
is constantly pumped into this by the force of the heart, it 
enlarges, and at length it may burst, and the life of the 
patient be destroyed by the loss of blood. When an aneu- 
rism formed in a limb, as for example in the ham, the 
surgeon, in former times, used to save the life of the patient 
by amputating the limb above the aneurism. Putting a liga- 
ture round the artery above the aneurism would of course 
stop the flow of blood into it ; but it was supposed that the 
limb would die, in that case, from the want of a proper 
supply of blood. 

But it was found, at length, that this was not so; and 
surgeons now, in such cases, cure the disease, and save the 
limb too, by tying the artery. Immediately after the opera- 
tion the limb is cold, and there is plainly very little circula- 
tion in it. But in a few hours the circulation becomes free, 
and in a little time it is as well established as ever. This 
is effected by the communications which exist between the 
branches which go off from the artery above the aneurism, 
and those which go off below it. It is obvious, however, 
that this would not be thoroughly effected if no change 
took place in the size of the communicating arteries. But 
this change does occur. Some of them become enlarged to 
meet the necessity of the case. 

This is a most interesting fact; and so is also the fact — 
that these communications between branches of arteries are 
very common in the neighborhood of those places in the 
body where aneurism, from strains produced by violent and 
sudden motion, is peculiarly apt to appear. This same pro- 
vision avails, of course, when aneurism is cured by pressure 
made upon the artery above it, a measure which modern 
surgery has found in many cases to be as effectual as tying 
the artery. 

136. Action of the Heart Illustrated.— There 
have been great differences of opinion among physiologists 
in regard to the proportionate amounts of agency that the 
different parts of the apparatus have in carrying on the cir- 



THE CIRCULATION. Ill 

dilation. The heart manifestly exerts the chief agency, 
both by its forcing and its suction power. You can get a 
clear idea of the manner in which it exerts these two forces 
in this way : Fill a ball of india-rubber, to which a tube is 
attached, with water, and immerse the tube in a vessel of 
water. If you press the sides of the ball together, some of 
the water is forced out into the vessel. This represents the 
contraction of the heart. If, now, you allow the ball by its 
elasticity to resume its round shape, the water rushes into 
it from the vessel. This represents the dilatation of the 
heart. 

The dilatation of the ball results from its elasticity ; and 
it is supposed by some that the dilatation of the heart 
results from the same cause, its contraction alone being 
produced by muscular action. Whether this is so or not, 
the dilatation is an active one, and the blood rushes into the 
heart from the veins by suction, as it is termed. The dila- 
tation is so active that, as has been shown by experiments 
on animals, even a great amount of pressure is not able to 
prevent its taking place. 

13 4 . Action of the Capillaries. — But, great as 
the agency of the heart is, it is not true that it is the only 
moving power, and that the arteries and veins are mere 
rive conducting tubes. There are various phenomena 
which show that the arteries, the capillaries, and even the 
lax veins, exert a considerable agency in circulating the 
blood. We will merely allude to some of these phenomena. 

Determinations of biood to particular parts show that 
the blood-vessels have an active agency in the circulation. 
In inflammation of any part, there is an increased activity 
lie particular portion of the circulating apparatus sup- 
plying that part. In the act of blushing, there is a local 
vity of the circulation somewhat independent of the 
heart. This is also true of the circumscribed flush of 
hectic. 

t38. Circulation in the Liner.— There La 
portion of the circulation in which the actrv 

capillaries is especially manifest. The veins, receiving 



112 



PHYSIOLOGY AND HYGIENE. 



the blood from all parts of the body, at length are all 
united into two veins, which empty their contents into the 
heart. But there is a very remarkable exception to this. 

The veins which collect the blood from the viscera in the 
abdomen unite in one large trunk, called the vena portae ; 
and this, instead of pouring its contents into the large vein 
that goes up to the heart, divides, like an artery, into 
branches, which take all this blood to the liver for the 
manufacture of bile. Fig. 68 represents this circulation 
of the vena portae. 1, 1, are the veins coming from the 
intestines ; 2 is the trunk of the vena portae ; and 3, 3, are 
branches of it distributed in the liver. 




CIRCULATION OF VENOUS BLOOD IN THE LIVER. 

There must be, in this case, some propelling power in 
the capillaries, and some, also, in the veins. If there 
were not, another subordinate heart would obviously be 
needed in the vena portae, to pump up the blood from all 
the veins of the abdominal viscera, and then to send it 
through all its branches into the capillaries of the liver. 



THE CIRCULATION. 113 

139. Why the Veins are Full and the Arteries 
Empty after Death. — The veins have a less active 
agency in the circulation than any of the other parts of 
the apparatus. It is for this reason that commonly after 
death the veins are found quite full of blood, while the 
arteries are nearly empty. The apparatus of the circula- 
tion may be regarded as forming a circle of organs in this 
order — the heart, the arteries, the capillaries, and the veins. 
The blood is constantly going the rounds of this circle. 

It is plain that, as the apparatus is about to stop, there 
must be an accumulation in the weakest, least active, and 
most relaxed of this circle of organs. The arteries and 
capillaries force the blood into the veins to the last moment 
of life. This effect probably extends no further than the 
smaller veins ; but the heart, by its active dilatation, draws 
the blood from them into the larger veins. And as these 
two forces, at the two ends of the venous system, are at 
work up to the last moment, the whole of this system is 
filled with blood. 

The fact that the large arteries are commonly found 
nearly empty of blood after death, gave the ancients the 
idea that air circulated in arteries, while blood circulated 
in veins.- Hence the name, artery, is derived from two 
Greek words, signifying to hold air. And hence, also, by 
long established custom in common language, the blood is 
spoken of as running in our veins ; and it would sound 
strangely if, in common and especially in poetical language, 
we should speak of it as running in our arteries also. Al- 
though there were from time to time some glimpses of the 
true idea of the circulation, it was not really developed and 
demonstrated till about two hundred and fifty years ago. 

140. Changes wrought in the Blood. — A step 
farther in the development of the plan of the circulation will 
now be taken. We have seen that the office of the arteries is 
t«> conduct the blood to the network of capillaries, and thai 
in the capillaries the blood hafi reached its place of destina- 
tion where it is to be nsecL The formative cells, appended 
to the capillaries, take from the blood what they need for 



114 PHYSIOLOGY AND HYGIENE. 

their various purposes, and at the same time there is added 
to the blood refuse matter from the waste of the tissues. 

The blood, then, is changed while it is in the capillaries. 
In the arteries it was red ; but, after passing through the 
capillaries, it appears in the veins of a purple color. It 
is also as much changed in other properties. It is no 
longer fitted to nourish the body. It would even prove a 
poison to any organ into whose capillaries it should flow. 
If, for example, it, instead of bright arterial blood, should 
be sent to the brain, that organ would cease to do its office ; 
insensibility would ensue, and life would soon be destroyed, 
if the flow of red blood could not be established. 

141. Change takes plaee in the Lungs. — This 
purple blood, which comes back to the heart from the 
capillaries by the veins, must, therefore, be in some way 
changed to red blood, before it is again sent all over the 
system through the arteries. This change is effected in 
the lungs. As the purple blood returns to the heart, it is 
sent by the heart to the lungs, in order to be exposed to the 
air before it is sent again over the system. For this purpose 
there is a second circulation, and the heart is made a double 
organ ; or rather, there are in effect two hearts for the two 
circulations, for the two sides of the heart have no com- 
munication with each other. The apparatus for all this is 
very complicated, but it can be made clear to you. 

142. Course of Circulation. — First examine dia- 
gram 69, which is intended to represent merely the course of 
the circulation, without regard to proportionate size of parts, 
or to minutiae in the arrangement of the apparatus. Let a 
represent the right side of the heart, c the left side, i the 
lungs, and d the general system of the body. The arrows 
show the direction in which the blood flows. In all the 
shaded part the blood is venous or purple, and in the part 
not shaded it is arterial or red. We will now trace on 
the Figure the course of the circulation. We will start at 
a, the right side of the heart. The blood received here, of 
a purple color, from the whole body by the veins, is sent by 
the heart to 5, the lungs. Here it changes to red blood, 



THE CIRCULATION. 



115 



and passes by veins back to the heart — but, observe, it is to 
the left side of the heart, c. It is now sent by this left 
half of the heart to all parts of the system, represented by 

Fig. 09. 




DIAGRAM SHOWING THE COURSE OF THE CIRCULATION. 

J. Here, in the capillaries, it is changed to purple blood, 
and goes back by veins to the right side of the heart, a, the 
place where we started. 

143. Two Circulations and Two Hearts. — 
You see, then, that there are two separate circulations, one 
through the general system, and the other through the 
lungs alone. In both circulations the blood is sent from the 
heart by arteries, and is brought back to it by veins. But 
notice that, while in the general circulation the red blood 
i< in the arteries, and the purple in the veins, in the eircu- 
lation through the lungs this is reversed — the red blood is in 
the veins, and the purple is in the arteries. So, also, while 
the change of the blood in the capillaries of the general 

in is from red to purple, in the capillaries of the lungs 
from purple to red. 

144. Valves.— There are not only two sides or ha! 

of the h< mated entirely from each other, but each of 

I wo apartments, with valves or folding-doors 
i them, so arranged thai the blood can pass one 
way through them, but not the other. There are also 
valves at the beginning of 1 1 artery of the heart, the 

aorta. Theg ed that the blood can go fr 



116 



PHYSIOLOGY AND HYGIEXE. 






Fig. 70. 




out of the heart into the artery, but not a drop can get back 
from the artery into the heart. There are similar valves 
also, at the beginning of the great pulmonary artery bj 
which the purple blood is sent from the heart to the lungs 
In Fig. 70 is represented a section of the right side of 
the heart, for the purpose of giving you an idea of the 
relative size and position of the two apartments. The 
auricle, a, so called because a part of it has some resem- 
blance to an ear, receives the blood from the whole sys- 
tem by two large veins, b, b, called the 
ventv cava. From the auricle it passes 
into the ventricle, v, which by its con- 
tractions sends it to the lungs through 
the pulmonary artery, /. The valve be- 
tween the auricle and ventricle is com- 
posed of three membranous sheets, which 
are held at their edges by small tendinous 
cords, cl, just as a sail is held by the ropes 
at its corners. This valve permits the 
blood to pass from the auricle into the 
ventricle ; but when it attempts to pass 
back from the ventricle to the auricle, 
it pushes back the sheets of the valve until their edges meet 
in the center, they being prevented from going too far back 
by the tendinous cords. 

There are also valves at e, the beginning of the pulmonary 
artery, which allow the blood to pass through them into 
the artery, but no blood can pass through them from the 
artery back into the ventricle. 

145. Relation between the Anrleles and 
Ventrieles. — The auricle and ventricle act in this way 
in propelling the blood. When the auricle contracts, the 
ventricle dilates* to receive the blood from the auricle. Th 
valves between them are open while this is taking place. 

* This dilatation is an active one, as was stated in 136, when speaking 
of the heart as a whole. The ventricle does not dilate because the 
blood is forced into it, but the blood rushes into it because it dilates. 



SECTION OF THE 

RIGHT SIDE OP 

THE HEART. 



THE CIRCULATION. 117 

But the next moment the ventricle contracts and the 
auricle dilates. If the valves between them should now be 
open, the blood would be forced back into the auricle. But 
the membranous sheets of these valves shut upon each 
other as the ventricle contracts, and thus prevent the blood 
from going back. It therefore is discharged through the 
pulmonary artery,/, the valves there being open. When 
the ventricle dilates, the blood would, from suction, enter 
it from the artery as well as from the auricle, if the valves at 
the orifice of the artery should remain open. They are ac- 
cordingly shut when the ventricle dilates. 

When, therefore, the auricle dilates and the ventricle 
contracts, the valves between the auricle and ventricle are 
closed, and those at the mouth of the pulmonary artery 
are open ; and, on the other hand, when the ventricle dilates 
and the auricle contracts, the valves between them are open, 
and those of the pulmonary artery are closed. 

Dr. Carpenter has a very good illustration of the relation 
of the actions of the auricle and ventricle, in a representa- 
tion given in Fig. 71- The apparatus which is represented 
consists of two pumps, a and b, the pistons of which move 
up and down alternately. These are connected with a pipe, 
in which there are two valves, d and e, opening in the 
direction of the arrows. The portion c of the pipe repre- 
sents the venous trunk discharging its blood into the heart, 
and the portion /, the artery which is the outlet for the 
blood. The pump, a, represents the auricle, and the pump, 
b, the ventricle. When the piston in a is raised, the fluid 
enters through c to fill it by suction, as it is termed. When, 
now, its piston 'is lowered, the fluid is forced through the 
valve d into the pump, b, (which represents the ventricle,) 
whose piston is at the same time raised to receive it. And 
when the piston in b is lowered in its turn, the fluid being 
prevented from returning into a, by the valve d, is forced 
through the valve e into /, representing the discharging 
tube, the artery. At the same time, a fresh supply ol fluid 
ived into a by the raising of its piston. 

The auricle and ventricle of one side of the heart, the 



118 



PHYSIOLOGY AND HYGIENE. 



right side, have been described. The left side is constructed 
very much in the same way. You will observe, in Fig. 70, 
that the ventricle is much more capacious than the auricle. 



Fig. 71. 



a 




cL 



f 



The auricle is indeed the antechamber to the ventricle, 
The ventricle, too, has much thicker walls. It is made 
very strong, because it does the principal part of the work. 
The size of the whole heart is about that of the closed hand 
of the individual. 

146. Valves of the Aorta. — Your attention is now 
called to a more particular view of the valves of the heart. 
We will take, first, the valves which are at the beginning 
of the aorta, the great artery of the body, going out from 
the left ventricle. These are very much like the valves of 
the veins seen in Fig. 67. There are three of them. They 
are like little pockets arranged around the orifice of the 
artery, and looking toward the tube of the artery. 

Of course, when the ventricle contracts, and forces the 
blood into the artery, these pockets are pressed by the blood 
flat against the sides of the artery. But when the ventricle 
dilates, and the blood attempts to go back from the artery 
into the ventricle, it gets into these pockets, and bulges 
them out toward the heart, and thus the mouth of the 
artery is closed. But if these pocket-like valves had plain 
curved edges, they would not effect a perfect closure. There 






THE CIRCULATION. 



119 



Fig. 72. 



would be a little space in the very middle of the orifice of 
the artery which would be left open. This is made plain 
by Fig, 72, which represents the orifice of the artery with its 
closed valves, as it would appear seen 
from the interior of the heart, if the 
three valves had plain curved edges. 
There would be a space left between 
them. But this difficulty is remedied 
by a very simple contrivance. A little 
fleshy projection is placed upon the 
middle point of the edge of each valve, 
of such a size that the three projec- 
tions together just fill the space A. 
When, therefore, the valves are closed, no blood can go 
back from the artery into the ventricle. This arrangement 
is shown in Fig. 73, in which the aorta, a, is laid open and 
spread, out, so as to show the three valves with their 
projections on the edges. At b and c, are the openings of 
the two arteries that supply the walls of the heart with 




Fig. 73. 




VALVES OF THE AORTA. 



blood for their growth and repair, for the heart is con- 
structed and repaired from its own blood. The valv. 
the orifice of the pulmonary artery are arranged in the 
same manner as those which are at the orifice of the aorta. 



120 PHYSIOLOGY AND HYGIENE. 

147. Arrangement of the Valves betiveen the 
Auricles and Ventricles. — The valves which are 
between the auricles and the ventricles, are folds of strong- 
white membrane, their edges being held by numerous 
small tendinous cords. And these cords are manned, as we 
may express it, by muscles attached to the walls of the 
heart. The office of these muscles is to hold on to the cords 
that are fastened to the edges of the valves, and prevent 
these sheets of membrane from flapping back too far when 
the powerful ventricle contracts. If this were not done, 
the consequence would be, that when the ventricle contracts 
with prodigious force, as sometimes occurs when the circu- 
lation is in a state of great excitement, the light tendinous 
fastenings would be ruptured by the pressure of the blood 
upon the valves. As arranged, however, the strong but 
yielding muscular bundles, to which these tendons are 
attached, regulate with great exactness the closing of the 
valves. 

148. No Valves at the Openings of the Vence 
Cavce. Why ? — In looking at Fig. 70, observe that, Avhile 
there are valves between the auricle and ventricle, and at 
the mouth of the artery going out from the ventricle, there 
are none at the openings of the two vence cava, the veins 
that pour their contents into the auricle. Why is this ? 
Why is there no need of valves here to prevent a regurgita- 
tion into these veins when the auricle contracts? It is 
because that, as the auricle contracts, there is at the same 
time the dilatation of the strong ventricle, making, of 
course, a suction in that direction so powerful as to counter- 
act most fully any tendency to regurgitation into the veins. 

149. General View of all the Parts of the 
Heart. — Having thus examined the heart in detail, you 
are now prepared to look at it as a whole. Fig. 74 presents 
a front view of the heart, in which a is the right auricle, 
receiving the purple blood from the whole body by two 
large veins, h and i, called the vence cavce ; b is the right ven- 
tricle, that receives the blood from the right auricle, and 
sends it to the lungs by the pulmonary artery, f; sis the 






THE CIRCULATION. 



121 



auricle, which receives the red blood from the lungs, bv 
pulmonary veins, g, g, g; d is the left ventricle thai 

receives the blood from the left auricle, and sends it all 

over the body through the aorta, c. 

You observe that you see but a part of the left auricle 

and ventricle, they lying partly behind the right ventricle. 

Fia. 74. 




FRONT VIEW OF THE HEART. 



You do not see the very beginning of the aorta, for, as it 
- from the left ventricle, it is at first concealed behind 
the top of the right ventricle and the beginning of the pul- 
monary art<ry. It then forms an arch, from which it sends 
forth branch'.- to the head and tipper extremities ; audit 
afterwards passes down behind the heart, to supply with its 
branches the trunk of the body and the lower extremities. 
6 



A.rJ.*J 



PHYSIOLOGY AND HYGIENE. 



In the line of division between the two ventricles, b and d, 
you see one of the coronary arteries, as they are called, which, 
coming from the beginning of the aorta, supply the walls of 
the heart with blood. 

150. Course of the Blood through the differ- 
ent Cavities of the Heart. — To make you quite fa- 
miliar with the relations of the different parts of this com- 
plicated organ, and with the course of the blood through its 
different apartments, in Fig. 75 is given a map of the 



Fig. 75. 



^i 




MAP OP THE CIRCULATION. 



heart, with the names placed upon the parts. The dark 
blood is received from all parts of the body by the vena cavce — 
from the parts above by the descending cava, and from the 
parts below by the ascending cava. These veins pour the 
blood into the right auricle. From this it passes into the 



THE CIRCULATION'. 123 

right ventricle, which sends it by the pulmonary artery to 
the lungs. From the lungs it returns by the pulmonary veins 
to the left auricle. It then passes into the left ventricle, 
from which it is sent by the aorta to all parts of the body. 

1 J 1. Bel at ion of the Heart to the Lungs.— In 
Fig. 76 is represented the heart, situated between the two 
lungs, with the arteries which carry blood from it, and the 
veins which pour their blood into it. The lungs are repre- 
sented as being drawn apart to the right and left in front, so 
as to expose fully the heart and its vessels. The sac con- 
taining the heart, and the packing cellular tissue, are re- 

Fig 76. 






/ ! ! i \ 




t ./ g it i 


LUNGS, 


HEART, AN J) PKIN( I PAL BLOOD-VESSELS. 



moved, so as to lay the heart and its vessels bare. At a is 
the trachea or wind-pipe; on each side of it are the two 
arteries, the carotids, which go to the head; c is the artery 
Which goes to the arm ; b, b, are the jugular veins coming 
from the head, d, d, the veins from the arms, all emptying 
their contents, ae • into the descending cava; e is the 

right auricle, receiving the blood from the two cavae ; / the 



124 PHYSIOLOGY AND HYGIENE. 

ascending cava ; g the right ventricle, i the left ventricle, 
and li the descending aorta. 

152. Causes of the two Sounds of the Heart. — 

The harmony of action between the two sides is preserved 
by having the two auricles act together, and the two ventri- 
cles act together. And this action produces two sounds, 
which may be heard by applying the ear to the left side 
of the chest. The first sound is rather a prolonged and 
heavy one, the second is light and quick. The first 
sound occurs when the strong action of the heart is per- 
formed, that is, when the ventricles contract. It is owing 
to several causes. One of these is the impulse of the heart 
against the walls of the chest. 

Another is the flapping together of the valves between the 
auricles and the ventricles, to prevent the blood from re- 
gurgitating into the auricles, when the ventricles contract 
to force out their contents. The light and quick second 
sound is caused principally by the flapping together of the 
valves at the mouths of the aorta and the pulmonary artery 
when the ventricles dilate. The pulse is produced by the im- 
pulse given to the blood by the contraction of the ventricles. 
There is, therefore, a pulse in the arteries of the circulation 
through the lungs, as well as in those of the circulation 
through the general system. Wherever there is an artery 
there is pulsation. 

153. Movement of the Heart as a Whole. — The 
impulse of the heart against the front wall of the chest on 
the left side is easily explained. The aorta, in going from 
the heart, makes an arch upward and backward, to go down 
in front of the spine ; and it is the tendency to straighten 
out, produced in this arch by the force of the blood thrown 
into it by the ventricle, that causes the throwing of the heart 
forward by a spring. This is easily seen as illustrated by 
Fig. 77, in which a is the spinal column ; 5, the front wall 
of the chest ; d, the heart ; and c, the arch of the aorta. 
When the heart throws the blood into this arched tube, 
tends to straighten it; but as the aorta is fastened to the 
fixed spine behind, there can be no impression made in 



THE CIRCULATION. 



125 



Fig. 77. 



that direction. The straightening of the arch must there- 
fore occur in the other direction, to the front ; and the 
heart is thrown a little forward, as represented by the dotted 
lines. The change of position thus produced is indeed but 
slight, but it is sufficient to cause the 
impulse. 

1 34. Per i c a r d i u m, — The 
heart is inclosed in a sac, called the 
pericardium., which, at its upper part, 
is fastened all around the vessels that 
proceed from the heart. This sac is 
lined on the inside by a serous mem- 
brane, which also lines the outside of 
the heart, being reflected over upon it 
from the pericardium. This mem- 
brane forms, therefore, a sac without 
any outlet. This is made plain by 

Fig. 78. In this diagram, showing the plan of the serous 
membrane of the pericardium, a, a, are the auricles; v, v, the 
ventricles ; b, c, the vessels proceeding from the heart ; p the 
serous membrane lining the outside of the heart ; p\ the same 
membrane reflected from the upper part of the heart and 




Fig. 78. 




L'-^> 



PLAN OF THE PERICARDIUM. 



covers the inside of the pericardium. Now, this sac is kept 
3t by a fluid exuding from its whole surface, so that, 



126 PHYSIOLOGY AND HYGIENE. 

as that part of it which covers the outside of the heart, in the 
motions of that organ, rubs against that part which lines the 
pericardium, the lubrication prevents any injury from the 
friction. This lubricating fluid is continually renewed, the 
exhalants and the absorbents balancing each other in their 
action. When the exhalants secrete more fluid than the ab- 
sorbents can take up, the excess accumulates, making what 
is called dropsy of the heart. 

155. Action of the Heart Involuntary. — The 
heart, as you have seen, is a complex arrangement of muscles. 
And these muscles are wholly involuntary; that is, they are 
not at all under the direct control of the will. No one can, 
by an exercise of the will, make his heart beat slower or 
faster. As will be seen in another chapter, this organ is kept 
at work by its nervous connection with the spinal marrow. 
It has no repose, as the voluntary muscles have, unless you 
call the intervals between the contractions and dilatations of 
its several parts intervals of repose. 

The amount of work which it does in a lifetime is enor- 
mous. The heart of an adult beats, that is, each one of the 
four chambers of this organ dilates and contracts, about 70 
times in a minute. This would make 100,800 times in 24 
hours, 36,792,000 times in a year, and 2,575,440,000 times in 
a life of 70 years. In children, the action of the heart is 
much more rapid, and in disease it sometimes reaches in 
them 160 or even 200 beats in a minute. 

The two circulations of the general system and of the 
lungs are ever going on. The blood is ever moving in all 
the cavities of the heart, in every artery, and vein, and 
capillary. It never stops till it is arrested by death. 

Note. — The heart moves in an ordinary lifetime, more than a quarter 
of a million of tons of blood. It can raise its own weight 20,250 feet in 
an hour. An active climber can accomplish only 4,000 feet an hour, 
or one twentieth of the work done by the heart, while the best locomo- 
tive can raise its own weight through only 2,700 feet in the same time. 




RESPIRATION. 127 



a ° 
1 ^ 



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CHAPTER IX. 

RESPIRATION. 

7.-7/J. Organs of Respiration* — The lungs are 
spongy filling up a large part of the chest, and sur- 

rounding the heart They are, in common language, the 



12S PHYSIOLOGY AND HYGIENE. 

lights ; and you can learn what they are in man by observing 
the lights of other animals. They are composed chiefly of 
air-tubes, air-cells, blood-vessels and nerves, packed together 
with the common packing material of the body, cellular 
tissue. The spongy lightness of the lungs is owing to the 
air-cells or vesicles. You can get some idea of the propor- 
tion of these cells to the solid part of the organs if you in- 
flate the lungs of some animal, as the sheep or calf, by blow- 
ing into the windpipe. These cells are exceedingly minute, 
and in them a marked change is effected in the blood. 

The capillaries holding the blood, branch out on the walls 
of the cells, and the blood is acted upon by the air through the 
pores of the vessels. The process of respiration introduces 
the air freely into these cells. The air enters through the 
windpipe, which branches out into tubes called bronchia 
which divide and subdivide, till they become very minute, 
and then end in the air-cells. These cells are estimated to 
be about the y^-th of an inch in diameter. Some calcula- 
tions have been made in regard to the extent of surface 
which they would all make if they could be spread out in 
one sheet. There is of course no great accuracy in such cal- 
culations; but we can readily see that the aggregate surface 
must be immense, and, therefore, the blood is thus very ex- 
tensively exposed to the action of the air. In Fig. 79 is 
represented the lung of one side, d; the branches of the bron- 
chi of the other lung, c, at the lower part of which, e, they 
are represented as they branch out minutely to open into the 
air-cells; b is the trachea or windpipe, and a is the larynx 
at the top of it. It is through a chink called the glottis, in 
the larynx, that all the air passes as it goes into and out 
from the lungs. This will be particularly described here- 
after. 

157. Relative Situation of the Heart and 
Lungs. — In Fig. 76, in the last chapter, you see repre- 
sented the relative situations of the heart and lungs, the 
lungs being somewhat separated, however, from the heart, 
to the right and left, in order to show that organ fully. In 
their natural position they are close to the heart, and cover 



RESPIRATION. 129 

up all of it, except a small portion in front and to the left 
side, where its beating is so plainly felt. Both the heart 




LUNGS AXD AIR-TUBES. 

and the lungs are suspended in the chest to the upper part 
of the walls of this cavity, and are fastened also to the spinal 
column in the rear. The large vessels of the heart, and the 
bronchi of the lungs, serve as the principal means of sus- 
pending these organs, as is shown in the Figure. 

LIS. Pleura. — The lungs are covered by a white, 
shining membrane called the pleura, which also lines the 
inside of the walls of the chest. This is always kept lubri- 
1 by a watery fluid, so that, as the lungs expand and 
the chest moves, the friction will be attended with no incon- 
venience or injury. 

tr>D. The lAings not Connected to the Walls 
of the Cheat* — Von may perhaps ask why, as the lungs 
follow the walls of the chesl in its expansion, they could 
not have been fastened to these walls throughout their whole 



130 PHYSIOLOGY AND HYGIENE. 

surface. The principal reason probably is that, if this were 
the case, the intimate vascular connection which would 
exist between the walls of the chest and the lungs, would 
expose the delicate texture of these organs more frequently 
to injury from external violence. As it is now, the effu- 
sion, or the inflammation, consequent upon a blow on the 
chest, is not apt to affect the lung in the neighborhood, 
because it has no direct connection with it by nerves and 
blood-vessels. 

160. Mechanism of Breathing— You are now 
prepared to see by what mechanism the air is alternately 
introduced to and expelled from the lungs. The chest 
incloses a large space, which can be made much greater by 
certain movements of its walls. 

It is this expansion of the cavity of the chest, effected by 
certain muscles, which causes the air to rush into the chest 
through the trachea, just as air rushes into the bellows 
when the space within is enlarged by the separation of their 
walls. 

In Fig. 80 is shown the framework of the chest. At 5, 5, 
is the spinal column, the grand pillar supporting the walls 
of this cavity. The ribs, c, c, go from this with a large 
curve round to the breastbone, #, in front. The ribs, how- 
ever, do not join directly with the breastbone, but there are 
cartilages intervening, as seen in the Figure. The collar- 
bone goes from this breastbone across to the top of the 
shoulder. The ribs are twelve on each side. The lowest 
two are attached only to the spine, and are called floating 
ribs. The whole is so constructed as to allow a very con- 
siderable expansion of the cavity. As the chest is kept in 
constant motion, lightness in its walls is an object of some 
importance ; and, at the same time, it is necessary that the 
structure should be a strong one, in order to effectually guard 
the lungs from injury. Both of these objects are secured, 
by having the walls in front and at the side composed of so 
many bones, well bound together by the muscles which 
move them. The cartilages which connect the ribs to the 
breastbone are a great safeguard. They give elasticity to 






RESPIRATION. 131 

the structure as a whole, and the ribs are not very liable to 
be broken, because of the yielding of the cartilages with 
which they are connected. 




16 1. Framework of the Chest. — This framework 
is filled out with connecting material, chiefly muscles, which 
effect the expansion of the chest in inspiration. First, there 
is a large expanse of muscle and tendon called the diaphragm, 
stretching across the lower part of the chest and separating 
its contents frem the contents of the abdomen below. The 
edge of this muscle is fastened to the spine behind, to the 
end of the breastbone before, and all around the lower ribs. 
It is arched upward ; and against its concave surface press 
upward the liver and stomach, while the lungs and the 
downward against its convex surface. The dia- 
phragm is reprea nted in Fig. 81. The ribs are cut away in 
to give a front view of the cavity of the cl 
. the lnnga and heart being entirely removed. D I) is 
the diaphragm, very high in the central portion, which is 



132 PHYSIOLOGY AND HYGIENE. 

tendinous, but descending very low at its edges at the sides 
and in the rear. 

Fig. 81. 




DIAPHRAGM. 

Front View. 

162. Inspiration and Expiration. — TheDia* 
phragm. — If all the muscular fibres in the diaphragm 
contract, the arch will be flattened, and thus the room in 
the chest will be enlarged. To occupy this additional space 
the air rushes in through the windpipe. This is inspiration. 
In expiration, the reverse movement takes «place — the arch 
of the diaphragm rises, and compressing the lungs, forces 
the air out of them through the trachea. In inspiration, as 
the diaphragm is flattened, it pushes down before it the stom- 
ach, liver, &c, and hence the pressing out of the abdomen, 
which is so sensibly felt, if the hand be placed upon it during 
the act of inspiration. In expiration, on the other hand, 
the abdominal walls retreat inward. These two opposite 
states of the arch of the diaphragm, and of the walls of the 
abdomen, are represented in Fig. 82. It is a side view, the 



RESPIRATION. 



L33 



ribs being cut away. c is the cavity of the chest, and a, 
the cavity of the abdomen. The diaphragm and the abdo- 
men are represented as they are in expiration. The dotted 

Fig. 88. 




DIAPHRAGM. 

Side View. 



line marks the flattening of the arch of the diaphragm, and 

the projection of the abdomen, as they occur in inspiration. 

It is supposed that in ordinary expiration, there is little, if 

muscular action — that, as the diaphragm, which in 

{ration pushed down the stomach and liver, and thus 
thrust out the walls of the abdomen, ceases to contract and 

tea, the mere elasticity of the parts below, and especially 
of the abdominal walls, restores the former condition of 

_- and so the diaphragm is carried upward, and expira- 
mlta When, however, the expiration is at all forci- 



134 



PHYSIOLOGY AKD HYGIEXE. 



ble, it is produced in part by the action of the muscles of 
the abdomen and some of the muscles about the chest. 

163. Other Muscles, besides the Diaphragm, 
Act in Inspiration. — While this dome-shaped muscle, 
the diaphragm, is the principal agent by which the chest is 
enlarged, there are other muscles which render assistance. 
In Fig. 83, a is the spine ; c, c, c, the ribs ; b, the breastbone; 
d, the collar-bone ; g, the diaphragm. You observe, on the 




c a h 

WALLS OF THE CHEST. 



right side of the chest, certain muscles, % extending from 
the spinal column in the neck to the first rib. When these 
contract, the effect is to raise the first rib, and all the others 
being attached to it, of course follow. As the ribs in Fig. 
80 slant downward from the spine toward the front, the 
result is, that all the ribs are carried together forward and 
upward. The result is the more effectually secured by 



RESPIRATION. 135 

muscles which pass from rib to rib, as seen at r, e 3 c\ 0, Fig. 83. 
In this Figure, the ribs, c. c> c> are left bare on the left side, 
to show the arch of the diaphragm, //, the dotted line indi- 
cating it on the right side. 

1(>4. Arrangement of Muscles between the 
liibs. — There are two layers of muscles connecting the 
ribs, the fibres of which cross each other, as represented at 
M, in Fig. 84. E II are parts of two ribs. The spaces 

Fig. 84. 




between the ribs are filled with muscular fibres, arranged as 
represented in the Figure. 

These muscles between the ribs not only help to raise all 
the ribs as a body, but they bring each rib nearer to the one 
above it. This increases the expansion of the chest, especi- 
ally as the ribs are so joined to the spine, that if a rib be 
moved upward, it must be carried outward as well as for- 
ward. It is evident that by the operations of these muscles 
in the neck and between the ribs, the diameter of the chest 
will be increased from front to rear, and also from side to 
side. 

The chest is expanded, then, by two motions — by flattening 

the arch of the diaphragm, and by raising the ribs. In 

ordinary quiet respiration, this expansion is effected chiefly 

by the diaphragm. But when there is a call for more active 

r Bpiration, as in violent exercise, the muscles which raise 

ribs act strongly, and hence the heaving of the chest, 

ailed. Their action is violent when from disease, as 

in asthma, for example, it is difficult to introduce sufficient 

ih" lung 

/ 7.7. Result of an Opening through the 

Wall of the Chest* — The lungs, heart, tourately 



136 PHYSIOLOGY AND HYGIENE. 



fill the chest in all the variations of size to which its cavity 
is subjected in respiration. For, when the chest is expanded, 
the spongy lungs swell out to follow its walls, and the air 
rushes in through the trachea to fill the expanding air- 
cells. If, now, there were an opening through the walls of 
the chest, communicating with the outside of the lung, 
when the chest expanded, the air would rush in at this 
opening as well as through the trachea, and the lung would 
be compressed in proportion to the freeness of the open- 
ing. This has sometimes occurred from disease and from 
wounds. If a free opening were made at the same time in 
both sides, both lungs would be compressed, and death 
w r ould be produced by suffocation, as really as if some 
obstruction in the windpipe prevented the air from entering 
the lungs. 

166. Change in the Blood effected in the Air- 
cells. — As has been said, the change in the blood, from 
purple to red, is effected in the air-cells. The blood and the 
air are brought very near together for this purpose ; and yet 
they are kept entirely separate. It is supposed that the air 
in the cells acts upon the blood through the pores of the 
vessels containing it, which branch out on the walls of the 
cells ; for if dark venous blood be inclosed in a bladder, the 
air will act through the pores of the bladder, and gradually 
change the outer portion of the blood to a red color. 

167 . Variable amount of Work done by the 
Air-cells. — These air- vesicles, then, do an important work. 
The change which is effected in them is immediately essen- 
tial to the continuance of health, and even of life. If the 
air be in any way shut out from them death occurs at onc^. 
And so important is it that they should do their work well, 
that extraordinary provisions are made to secure an abun- 
dance of room for them under all circumstances. For the 
cavity of the chest, as you have seen in this chapter, can be 
expanded to a very great extent. It would indeed be diffi- 
cult to conceive how a greater range of expansion could be 
secured. As the air-cells are called upon to do more work 
at some times than at others, there are special provisions for 



, 



UESPIitATlON. 137 

a larger dilatation of the chest than is required in ordinary 
quiet respiration. Thus when, from violent exercise, the 
blood is coursing rapidly through the lungs, and more air is 
therefore needed to change it to red arterial blood, the chest 
is largely expanded by calling into action muscles, which do 
but little, if any thing, in ordinary breathing.* 

tG8. Injury done to the Air-cells by Com- 
pression of the CJtest. — As the apparatus of respiration 
i especially arranged to secure room for the lungs under 
all circumstances, it must be very deleterious to the health 
of the body to interfere with this arrangement. If the ex- 
pansion of the chest in breathing be limited by any pressure, 
every air-cell must be embarrassed in doing its part in 
changing the blood. 

Either all of them must be unduly contracted, or some of 
them must become obliterated, so that there will not be as 
many vesicles as there should be. In either case, the organ 
is disabled in proportion to the amount of the compression. 
The blood is not so good as it would be if there were enough 
vesicles, and they could perform their work without con- 
straint. The vigor of the system is therefore lessened. And, 
besides, the lungs themselves, from this unnatural confine- 
ment, are especially liable to disease, j 

Vigorous exercise undoubtedly causes much injury to 
lungs that are thus confined. If the chest be left free to ex- 

* It is a curious fact that the mechanism of respiration is somewhat 
different in the two sexes. In men the diaphragm takes the larger 
share in the process, the upper ribs moving comparatively little ; in 
women the reverse is the case, the respiratory act being largely costal. 
— IIuxj.i 

\ The volume of air which remains in the lungs (Residual air) after 
& forced expiration, is from 75 to 100 cubic inches. An equal additional 
volume (Supplemental air) remains in the chest after an ordinary ex- 
piration. 

In ordinary breathing, 20 to SO cubic inches (Tidal air) pass in and 
inspiration will add 100 cubic inches (Complemental air) 
Line. Then after a forced u 3 contain 100 - 

1 cubic inches of air. After an ordinary inspin 
100-100 I cubic inch 



138 PHYSIOLOGY AND HYGIENE. 






pand to its fullest extent when occasion requires, this injury 
is avoided. For when the strongly and rapidly contracting 
heart pumps the blood in such quantities into the lungs, the 
widely expanding chest draws in the due amount of air to 
change the extra amount of blood. All the air- vesicles are 
ready to do their duty, and, therefore, no violence is done to 
the delicate texture of the lungs. 

But if these organs be compressed, the dilatation of those 
vesicles that are not obliterated, in the midst of the commo- 
tion of the difficult respiration, is very unequally effected, 
and some of them are stretched beyond their proper dimen- 
sions. At the same time, the blood must be here and there 
obstructed in its passage through the lungs, producing what 
is termed congestion. And if this violence be frequently re- 
peated, permanent disease will be the result. 

From the considerations in the last two paragraphs it is 
manifest, that the interference with the due expansion of 
the lungs, which so commonly results from the modes of 
dress in the female sex, must be one of the prominent causes 
of consumption, to say nothing of other diseases arising from 
this cause. 

This interference is effected in two ways — chiefly by com- 
pression of the chest directly, but also by the pressure which 
the load of clothing hanging from the waist must make 
upon the upper part of the abdomen. This latter cause 
interferes with that forward movement of the abdomen 
which is necessary to the flattening of the arch of the dia- 
phragm in the act of inspiration. 

The extent to which compression of the chest is some- 
times carried is seen by comparing the two outlines in Fig. 
85. One is an outline of the Venus de Medicis, the univer- 
sally recognized beau ideal of beauty of form in the female, 
and the other is an outline of the form of a lady with an 
artificially small waist. In Fig. 86 is represented the frame- 
work of the chest of its natural size, and as it is sometimes 
contracted by fashion. The Figures representing the con- 
traction of the chest may appear at the present time as cari- 
catures, for a very small waist is not considered now to be so 



' 



RESPIRATION. 



139 



itial to beauty in the female form, as it was twenty-five 
years ago. The truth, as uttered by medical men, has had 

• effect But the evil is remedied only in part. The 
chest of the female is still too much begirt, in obedience to 



Fro. 85. 





the tyranny of fashion, to allow of the free expansion to 
secure which such special pains are taken by nature. The 



Fig. 





evil begins in childhood. The chest is moulded during its 

wth to the shape which fashion prescribes. It could not 

9t has attained its full size. The torture 

of th do it could not be endured. 

In childhood, therefore, while the boy's chesl is lefl to 

natural shape and dimensions, the girl is begirt 



140 PHYSIOLOGY AJs T D HYGIEKE. 

so tightly as to embarrass her respiration, because nature is 
too ungenteelly large in her patterns, 

l(ii)> Cause of Death in Drowning* — It is the 
interruption of the change which is effected by the air upon 
the blood in the lungs, that produces death in drowning. 
The very common supposition, that considerable water gets 
into the lungs in drowning, is erroneous. Very little water 
ordinarily gets in — not enough to occasion any embarrass- 
ment. 

The difficulty is, that the air is kept out, and not that the 
water gets in. The drowning person makes attempts to 
inspire, but the moment that the water reaches the epiglottis, 
the door of the windpipe, it causes at once, by its irritation, 
a spasmodic closure of the epiglottis, so that almost no 
water is introduced. In the mean time, the purple blood 
continues to be thrown by the right ventricle of the heart 
into the lungs. But the little air contained there soon 
parts with its oxygen; and then the change in the blood 
ceases to occur, and dark blood is sent from the lungs to 
the heart, and thence to all the organs. These can Dot 
go on to do their duty without the stimulus of arterial 
blood. 

The brain, therefore, gives out, and there is insensibility. 
The muscles cease to act, and all motion is gone. If a good 
supply of arterial blood could be furnished to all the organs 
until breathing could be again commenced, life would be 
preserved, and there is provision for such a supply in cer- 
tain animals that can remain under water for some time. 

170. Singular Provision in the Whale.—For 
example, in the whale there are large reservoirs for contain- 
ing arterial blood, which can be used for the supply of the 
organs while he remains under water. When the supply 
begins to be exhausted, the animal of course has those 
uncomfortable sensations which a predominance of purple 
blood is so apt to produce. He manifests his uneasiness by 
his puffing and blowing, as he rises to the surface to get a fresh 
supply of air, and with it a fresh supply of arterial blood in 
the reservoirs. 



RESPIRATION. 



141 



171. Respiration in Fishes. — The apparatus of 

i rat ion varies in different animals. It appears in three 
as — lungs, gills, and tracheae or air-tubes. The gills of 
the lish are arranged in fringed lamina', in order to present 
by all their minute divisions a large surface : 
and these delicate organs are covered with a lid F» 
to protect them from injury. The blood-vessels, 
which contain the blood to be changed, branch 
out on the surface of the fringes of the laminae, 
just as the blood-vessels in lungs branch our 
on the surface of the air-vesicles. The air 
which is to change it is mingled with the water. 
It acts upon the blood, as the water containing 
it, after being taken into the month of the fish, 
368 out through these lamina?, as through a 
sieve. That the air in the water is the cause 
of the change can be proved by experiment. 

If a fish be placed in a vessel with its orifice 
closed, so that no air can enter, it will soon die 
from suffocation, because the air in so small a 
portion of water is soon used up. Although 
the fish can not with his gills use air that is not 
mingled with water, it is supposed that it is 
merely because the gills soon become dry when 
exposed to the air, and that the air would act 
on the bh»od in the gills if they were only kept 
moist. Indeed, in the land-crab, that has the 
power of living for some time out of the water, 
it has been found that there is a gland in the 
gill-chamber which furnishes a secretion tokc; -p 
gills moist. 

Gills differ mnch in their -hap 'and arrange- 
ment in the various aquatic animals. In Pig. 
d the arenioola or lob-worm. 
If re th gills are in the form of tufts arranged 
along tl the body. They take a Bomewhal Bimilar 

i in the larva- of many aquatic insects, ae - en in Fig. 
88. A large surfae i to the air contained in the 



LOB- WORM. 



142 PHYSIOLOGY AND HYGIEXE. 

water by the delicate and beautifully arborescent gills of 
these animals. 
Fig. 88. 172. Respiration in Insects. — In in- 
sects, we find the respiration effected by trachea 
or air- tubes. These go into all parts of the body, 
and the air contained in them acts upon the 
blood in the tissues of the body. The insect, 
therefore, has no distinct respiratory organs 
situated in any one part of the body, but the 
air is carried into every part. This seems to be 
necessary on account of the feeble circulation 
in the insect. 

The tracheae which, as Cuvier says, conduct 
1TTT3 , the air in search of the blood, as the blood has 

LARVA OF THE 

mayfly. no means of travelling in search of air, open on 
the surface by stigmata, as they are called, which are of 
various shapes and number in different insects. In the 
grasshopper there are twenty-four, arranged in four rows. 
You can suffocate an insect by simply covering the stigmata 
with varnish. 

In Fig. 89 are represented the trachea in an insect, the 
nepa or water-scorpion. The tracheae, as you see, send 
branches out in every direction, so that air is introduced 
into every part of the body. There are lungs, so to speak, 
everywhere in the insect. 

173. Respiration in Birds. — The apparatus of 
respiration is largely developed in birds for two objects — to 
provide for the extensive change in the blood which is re- 
quired by their great activity, and to give lightness to the 
body. 

To secure these objects there are air-sacs connected with 
the lungs, and located in different parts of the body ; and in 
birds that fly rapidly and are long upon the wing, these sacs 
are very extensive, and even many of the bones are made 
hollow, and are connected with the air-sacs. 

By this arrangement, the air is introduced extensively to 
the blood in the capillaries on the walls of these sacs, and at 
the same time the body is made very light. And the heat 









RESPIRATION. 



143 



generated by the effort of flying must expand the air in the 

air-sacs and swell them out, and thus make the body lighter. 
In Fig. 90 is seen this arrangement of air-sacs in the ostrich. 
The lungs, /, I, are quite small, but the air-sacs, c, c, c, are 
very large. The orifices by which they communicate with the 
lungs are as shown in the Figure. In birds of great powers of 

Fig. 89 



1st PAIR OP 
LEGS. 



WTXG CUT OFF, 



2D PAIR OP 

LEGS. 



3d PAIR. 




RESPIRATORY APPARATUS OF THE WATER-SCORPION. 

Bight, the air-sacs are much more extensive. This arrange- 
ment of air-sacs in different parts of the body of the bird 
►me analogy to the trachea) distributed in the bodies 
of insec 



144 



PHYSIOLOGY AND HYGIENE. 



174. Changes produced in the Air in the 
LunffS.— You have seen that the object of the apparatus 
of respiration is to change venous blood into arterial, and 
you have also seen how the air is introduced to the blood in 
order to effect this change. 




LUNGS OF THE OSTRICH. 

And now the interesting inquiry arises, what are the 
actual changes which occur, both in the blood and in the 
air, in the lungs. If you take a tumbler filled with lime- 
water, and breathe into it through a tube, the lime-water will 
become turbid, and will soon deposit a sediment. This is 
chalk, or carbonate of lime, formed by the union of the car- 
bonic acid gas exhaled from the lungs with the lime in the 
lime-water. Whence comes this carbonic acid gas, and how 
is it formed ? In order to answer this question satisfactorily. 






KESPIRATIOX. 1-15 

wo must learn something of the chemical constitution of the 
air which we breathe. 

It is composed of two gases, oxygen and nitrogen. In 
every 100 parts of common air, there are 79 parts of nitrogen 
and *21 of oxygen. It is found that the oxygen is that con- 
stituent of the air which is necessary to life. If an animal 
be placed in a closed jar tilled with common air, he will soon 
die. and the oxygen will be found to have disappeared, while 
the nitrogen will remain very nearly as at first. 

If, now, one animal is placed in a jar of nitrogen, and 
another in a jar of oxygen, the one in the nitrogen will die 
immediately, while the other will be very lively until the 
gen is mostly used up by his lungs. The animal in the 
pure oxygen will breathe at first more rapidly than the animal 
in the jar of common air ; and it is thought that oxygen is 
too stimulating for the lungs, and therefore needs to be 
diluted with the nitrogen, since the latter is always found in 
the air that we breathe. 

17 o. Change takes place in the Capillaries.— 
In the case of both the animal in the jar of air, and that in 
jar of oxygen, carbonic acid is found to have taken 
the place of the oxygen which has disappeared. This gas is 
made by a union of oxygen with carbon or charcoal. It was 
formerly supposed that this union is effected in the lungs — 
that carbon is thrown off from the venous blood in the lungs, 
and that the oxygen of the air there unites with it, and so 
carbonic acid appears in the air expired from the chest. 
But it has been discovered that the exchange is not made 
in the lungs. The oxygen is absorbed by the blood, and 
goes with it to the heart to be sent all over the system. 
And it is in the capillaries that the oxygen unites with 
carbon to form carbonic acid. 

The union takes place while the blood is changing from 

rial to venous, and is an essential part of the change. 

carbonic acid thus formed in the capillaries, is brought 

■ the heart in the venous blood, and is discharged 

from the system in the lungs. That the change takes place 

d has been abundantly proved in various wa 



146 PHYSIOLOGY AND HYGIENE. 

It has been found by experiments which will not be de- 
tailed, that carbonic acid exists in considerable amount in 
venous blood ; while, on the other hand, there is much oxy- 
gen in arterial blood. The inference from this is, that oxy- 
gen unites with the blood as it passes through the lungs, 
goes with it to the capillaries, and there unites with the 
carbon, giving us the carbonic acid which we find in the 
blood in the veins, after it has passed into them from the 
capillaries. 

It has been found, also, that if frogs or other cold-blooded 
animals be placed in hydrogen or nitrogen (gases which 
produce no injurious effect on them) they will give off for 
some time nearly as much carbonic acid as they would have 
done in common air. 

In this case, as no oxygen is introduced into the lungs, 
the carbonic acid cannot come from any union effected in 
these organs between carbon and oxygen, but it must be 
discharged by exhalation from the blood as it is passing 
through the lungs. Of course the discharge of the carbonic 
acid ceases after a little time ; for, there being no new supply 
of oxygen by way of the lungs, as there is when the animal 
is breathing common air, there can be no new formation of 
carbonic acid. 

But even cold-blooded animals can not live in these gases 
for any great length of time, for oxygen is needed for the 
continuance of their functions. And in the warm-blooded 
animals, a constant supply of it is necessary — they will 
die if cut off from this supply even for a short time. 

176. Changes produced in the Blood by the 
Air. — The change which takes place in the blood as it 
passes through the lungs, occurs to som'e extent when the 
blood is exposed to the air in any way. Thus, if blood be 
drawn from a vein into a bowl, the surface of it becomes red 
by the action of the air upon it. Carbonic acid is discharged 
from it, and the oxygen of the air takes its place, uniting 
with the blood, just as the process occurs in the lungs. A 
larger part of the blood will be thus changed, if it be shaken 
so as to expose more of it to the air. The change takes place 



: 



RESPIRATION. 11? 

3ome extent even if a membrane be interposed, as when 
the blood is inclosed in a bladder. The oxygen of the air, 
in this ease, is introduced through the bladder, and the car- 
bonic acid gas escapes through it. Precisely in this way is 
the change effected in the lungs, as already slated. 

The biood is separated from the air by being confined in 
blood-vessels, and the air in the vesicles acts upon it through 
the walls of these vessels. And, as the blood is divided into 
innumerable little streams, every part of it is acted upon by 
the air in the vesicles. Though the texture of the lungs is 
xlingly delicate, yet the blood is confined to its limits, 

d though it courses through these organs with great 
rapidity, and it never mingles with the air except as a con- 

lence of actual disease. 
17 7. Quantity of Carbonic Acid r/icen out 
bif the Lungs. — The quantity of carbonic acid discharged 
from the lungs in the course of twenty-four hours is very 
great. Many experiments have been tried and calculations 
made to ascertain its amount, from which it is estimated 
that there is at least three-quarters of a pound of charcoal in 
the carbonic acid thrown off from the lungs of a common- 

I adult in the course of twenty-four hours.* 
178. Necessity of Ventilation. — This gas is a 

lly poison. When accumulated in a considerable amount, 
as when charcoal is burned in an open furnace in a close 
room, it may prove immediately destructive to life. And in 

very prevalent neglect of ventilation, the frequent ac- 
cumulation of this gas from the respiration must prove more 
or less injurious to the health. 

Whenever the proper amount of oxygen gas is withheld 

: the lungs, and carbonic acid takes its place, the quality 
of the Mood is impaired from incompleteness of the change 

ted in the lungs, and the vigor of the body must in this 

- ned, to say nothing of the deleterious influence 

of this gas upon the nervous system. Though the results 

* Three-fourths of a pound of curbon united with oxygen will form 
two and three fourths pounds of carbonic acid. 



148 PHYSIOLOGY AND HYGIENE. 






are not immediate and palpable, great injury is continually- 
done to the health of multitudes by the accumulation of this 
gas, in small close apartments, and in crowded assemblies. 

A congregation of twelve hundred people throw off from 
their lungs in two hours an amount of carbonic acid that 
contains seventy-five pounds of charcoal. And yet little 
pains is commonly taken to carry off this vast quantity of 
poisonous gas, and replace it with pure air. * 

179. Carbonic Acid Exhaled from the Lungs 
of Animals Absorbed by Plants. — As so much oxy- 
gen is absorbed in the lungs of all animals, and so much car- 
bonic acid is thrown out from them, the inquiry arises how 
the air is replenished with oxygen, and is cleared of the car- 
bonic acid which is thus so largely mixed with it. It is 
found that this is accomplished, to a great extent at least, 
by the leaves of plants. The process which goes on in these 
lungs, as they may be called, of the plants, is quite the re- 
verse of that which is going on in the lungs of animals. 

The carbon of the carbonic acid which is thrown off from 
the lungs of animals is absorbed by the leaves of plants, and 
the leaves replenish the air with the oxygen, which is so 
constantly and abundantly absorbed in the lungs of the ani- 
mal creation. Thus the animal and vegetable kingdoms are 
sources of supply to each other. 

It may be thought that there would be a surplus of oxy- 
gen in the atmosphere in warm climates, where the vegeta- 
tion is so luxuriant; while, on the other hand, there would 
be an accumulation of carbonic acid gas in the colder regions. 
This would be so, if the air were not so movable that the 
equilibrium is readily secured in either case. 

1 80. Light Necessary. — It is an interesting fact, 
that the presence of light is necessary to the process which 
has been described as going on in the leaves of plants. Each 
leaf may be considered as a laboratory, and the light as the 

* It is estimated or perhaps determined that each individual ought 
to have at least 800 cubic feet of space to himself, this space to be 
constantly supplied with pure air, with provision for the exit of the 
foul air, or — in other words — this space to be perfectly ventilated. 



RESPIRATION. 119 

chief agent in effecting the chemical changes that occur in 
it. And it is found that no artificial light can do the work. 
It is only the light of the sun that is competent to this 
chemistry. 

And as these innumerable laboratories are everywhere at 
work, absorbing the carbon and exhaling the oxygen, to 
purify the air rendered noxious by the laboratories of the 
animal creation, we must confess it to be a mystery how 
the chemistry of the lungs of animals and that of the 
leaves of plants should be kept so nicely balanced. The 
balance is so strictly maintained, that the chemical compo- 
sition of the air is always found to be almost exactly the 
same. 

18 1. Animal Heat.— The heat of the body is main- 
tained by the union which takes place in the capillaries 
between the carbon and hydrogen of the system, and the 
oxygen which is introduced into the blood through the 
lungs. It is a process analogous to combustion. When 
carbon or charcoal is burned in a vessel containing air, the 
oxygen unites with the carbon, and carbonic acid gas is 
formed. 

The same union occurs in this case between carbon and 
gen that we find occurring in the capillaries. A sort of 
combustion is going on in every part of our bodies. And, 
as heat is evolved in the one case, so it is in the other. 
The same can be said of the burning of hydrogen and oxy- 
gen together. Heat is caused by the union thus produced 
between them, and so it is when they unite in the body. 
The water which is exhaled from the lungs comes from this 
union of oxygen and hydrogen. 

It wits formerly supposed that the union between the oxy- 
gen and the carbon and hydrogen takes place in the lungs, 
and that the heat is made there, and then is distributed over 
whole system. But it was objected to this supposition, 
that it made the lungs a sort of furnace for the rest of the 
body, and that, if the supposition were correct, there ought 
to be a much higher degree of heat in these organs than 
anywhere else, which is not the case. It was at length dis- 



150 PHYSIOLOGY AND HYGIENE. 

covered that the unioji between the oxygen and the car- 
bon and hydrogen occurs in the capillaries of the body 
instead of the lungs; that the combustion that produces 
the heat occurs throughout the system, instead of in one 
locality. 

182. Three Sources of Fuel.— The fuel for this 
combustion comes from three sources. One of these is the 
waste of the tissues. This furnishes a considerable amount 
of the carbon and hydrogen for the union with the oxygen, 
in all animals that are subjected, from their activity, to much 
wear and tear of the system. 

Another source of the fuel for combustion is food. The 
oils, sugars, and starchy kinds of food are devoted in a great 
measure to this particular purpose. These furnish a sort of 
floating fuel, as we may express it, which is carried about in 
the blood. Hence, we see that our diet must necessarily be 
varied according to the weather and the climate. 

In cold weather the heat of the body is more rapidly 
abstracted than in warm weather, and, therefore, we need 
then more of that food which affords a supply of carbon and 
hydrogen. Similarly, the enormous quantity of oily food 
often consumed by inhabitants of very cold climates is 
burned, as we may say, in the capillaries to keep up the 
animal heat. Of course, keeping the body warm by fire 
and clothing relieves from the necessity of taking any large 
quantities of fuel-making food. In the most favorable cir- 
cumstances there is a need of variation in diet to suit the 
weather and the climate, and we make this variation for the 
most part instinctively. Indeed there is a marked provision 
in nature for it. 

While there is a large amount of fat in the bears and seals 
and whales which afford food for the Esquimaux and Green- 
lander, there is very little in the animals which furnish a 
part of the diet of the inhabitants of tropical climates. 

Still another source of animal heat is the store of fat 
which is laid up in the body. One design of this accumu- 
lation of fat in different parts of the body seems to be to 
provide for the heat when other sources fail. Thus, when 



RESPIRATION'/ 151 

disease destroys the appetite, and thus cuts off the supply 
of food, the fat wastes away, or rather is burned up, to keep 
up the temperature of the body. The fat is the great means 
of maintaining the requisite temperature when hibernating 
animals become torpid for the winter. They become very fat 
in the autumn, before crawling into their winter quarters, 
and in the spring they come out very lean, their fat having 
1 consumed in keeping up even the low degree of tem- 
perature required during this time. 

183. Animal Heat differs in Cold and 
Warm-blooded Animals. — As the amount of heat 
produced, when charcoal is burned in air, or when oxygen 
and hydrogen are burned together, depends upon the quanti- 
ties of carbon and hydrogen that unite with the oxygen, 
BO, also, the degree of animal heat depends upon the quanti- 
ties of carbon and hydrogen that unite with the oxygen in 
the capillaries. This may be illustrated by referring to the 
effects of exercise on the heat of the body. 

When the circulation is quickened by exercise, the blood 
passes more rapidly than usual through the lungs, the respi- 
ration is consequently quickened, more air is introduced 
into the lungs, and therefore oxygen is more rapidly ab- 
sorbed by the blood. At the same time, the action of the 
muscles effects a waste of their tissue, so that more car- 
bon and hydrogen are ready to be released to be united 
with the increased oxygen. Hence comes the heat produced 

So, too, those animals which are the most active, ordi- 
narily have the most animal heat, and have the most exten- 
respiratory apparatus, so that there may be a free supply 
of absorbed oxygen to unite with the carbon and hydrogen 
of the changing tissues. It is in birds and insects that this 
onion takes place most largely, and in them, therefore, the 
>ry apparatus is very largely developed. This is made 
ry by their muscular activity, which produce* 
much waste matter thai must be removed from the system. 

Ad-blooded animals, on the other hand, are very inac- 
tive. There is not, therefore, much wear and tear of the 






152 PHYSIOLOGY AXD HYGIENE. 

tissues. There is comparatively little waste, therefore, to be 
thrown off. And so but little oxygen needs to be intro- 
duced into the lungs, and consequently little heat is gener- 
ated. To realize fully the contrast between the warm- 
blooded and the cold-blooded animals in these respects, 
observe, as the representative of the one class, a canary bird, 
and a frog as the representative of the other. 

The frog is generally quiet, and only now and then takes 
a leap, or croaks ; but the bird is ever in restless motion, and 
sings much of the time with all his might. The bird is 
warm with the heat generated by the constant union of 
oxygen with carbon and hydrogen in its capillaries ; but 
the frog is nearly as cold as the water in which he is im- 
mersed. The bird breathes rapidly, to let the oxygen of 
the air largely into his lungs ; but the frog seems scarcely 
to breathe at all, so scanty is the supply of oxygen which 
he needs. 

184. Uniformity of Animal Heat in the 
Warm-blooded Animals. — Cold-blooded animals 
are very nearly of the same temperature with the substances 
that are around them ; but warm-blooded animals have a 
certain degree of temperature, which they maintain with 
considerable uniformity under all variations of temperature 
in the atmosphere. This in man is about ninety-eight 
degrees Fahrenheit. This is above the temperature of the 
surrounding air, except in exceedingly hot weather. The 
human body is therefore always giving off heat. 

But the amount of heat which the human body can bear 
for a short time is much greater than the facts above alluded 
to would lead us to suppose. It was long taken for granted, 
that it could not safely bear, even for a short time, a heat 
much higher than that which is endured in hot climates. 
The truth on this subject was at length discovered by acci- 
dent. 

185. Interesting Experiments. — Two French- 
men were employed by government, in 1760, to devise some 
method of destroying an insect which infested the grain at 
that time. The result of their experiments was the dis- 



RESPIRATION. 153 

covery. that by subjecting the grain to a certain degree of heat 
in an oven the insect was destroyed, while the grain was not 
injured. While they were trying their experiments, a girl 
offered to go into the oven and mark the height of the 
mercury in the thermometer. It stood at 260°; and, after 
remaining there for ten minutes, which she found that 
she could do without any great inconvenience, she marked 
it at 288°, that is, 76° above the boiling point of water. 

These facts led to the famous experiments of Dr. Fordyca 
and Sir Charles Blagden, in England. With wooden shoes, 
tied on with list, they went into a room in which the ther- 
mometer showed the air to be at 260°. Their watch-chains 
were so hot that they could scarcely touch them, and eggs 
were roasted hard in twenty minutes, and beefsteak was 
cooked in thirty-three minutes. And yet the same air that 
produced these results was breathed by them with impunity, 
and it raised the heat of the body but very little. 

The air which was breathed out from the lungs was so 
much cooler than the air of the room, that it was refresh- 
ingly cool to the nostrils, and to the fingers as they Mowed 
upon them. In such cases, the evil effects of the heat are 
prevented chiefly by the great amount of perspiration that 
occurs, the vaporization of this abstracting the heat, which 
would otherwise accumulate in the body and produce dis- 
astrous results. The exhalation from the lungs, also, has 
Borne influence. 

186. Different Degrees of Torpor in Hiber- 
nating Animals. — In the state of hibernation, to which 
reference has several times been made, the torpidity varies 
in degree in different animals. In c.ild-blooded animals, res- 
piration and circulation may, in this state, cease altogether. 
In them the movements of life are often, perhaps we may 
generally, as fully suspended as they are m the seed that 
is kepi from heat and moisture. They may be preserved in 
this Btete for a long time and yet revive. 

B orpents and frogs have been kept in an ice-hoase f<n- 

. and then have been revived on being brought 

out into a warm atmosphere. In the warm-blooded animals 



154 PHYSIOLOGY AND HYGIEKE. 

that hibernate, the torpidity is less deep than in those which 
are cold-blooded. In them the respiration and the circula- 
tion become very slow, but never entirely cease. Indeed 
some species take food with them into their winter quarters, 
and occasionally wake up sufficiently to eat. But most of 
them are in a quiet, deep sleep, from which they do not 
arouse at all till the winter is past. 

In this state, as life is nearly, sometimes quite, at a stand, 
there is little wear and tear, and therefore little change in 
the tissues, and so there is need of the introduction of but 
little oxygen by the respiration. Dr. M. Hall, in his experi- 
ments and observations, found that the bat, w T hen completely 
torpid, consumed no oxygen, and discharged no carbonic 
acid from the lungs, although its circulation was not entirely 
suspended. 

187. Relation of Activity to Quantity of Air. 
The more active is the respiration of animals, the less able 
are they to bear a deprivation of air. A warm-blooded land 
animal will die if it be under the water only a few minutes ; 
but a cold-blooded animal can live under the water for some 
time, because it is not in so urgent need of oxygen. And, 
for the same reason, a w T arm-blooded animal, in a state of 
hibernation, may be kept under water for a long time with- 
out destroying life, although when in its active state it would 
die on being kept under w r ater for only a few minutes. 

188. General Summary. — The extensive play 
which the respiration has in the vital operations of the 
system has been shown. You have seen what the chemi- 
cal changes are, which it effects directly in the lungs, 
and indirectly in the system. And you have seen how 
the animal heat is produced by these changes, and how 
it is so regulated, that it seldom varies from its fixed 
standard. But it is to be remembered that, while the 
lungs, and even the capillaries everywhere are thus chemi- 
cal laboratories, the nervous system exerts a constant 
influence upon this chemistry of the body. This is espe- 
cially seen in regard to the production of heat, but it is 
true of the whole range of the chemical operations. The 



FORMATION AND REPAIR. 155 

laboratories would all cease their work if their nervous con- 
nections were destroyed.^ 



CHAPTER X. 

FORMATION AND REPAIR, 

189. Formative Cells appended to the Ca- 
pillaries* — The building and the repairing of the various 
structures of the body are done by vessels appended to the 
capillaries. The capillaries having received from the arte- 
ries the blood, the building material, the formative vessels 
Select from it, while it is in these capillaries, whatever they 
need for their purposes. Those vessels which, for example, 
form bone, select from the blood very different constituents 
from those which make nerve or muscle. 

190. Concert of Action.— These builders of the 
body not only have the power of selecting their building 
mat "rials from the blood, but they w r ork in concert. Each 
company of builders work together in harmony, as if they 
were under intelligent leaders. And though different com- 
panies may be in close proximity, there is no disagreement 
nor interference. For example, the builders of a tooth and 
the builders of the gum around it, do not encroach on each 
other: but each do their appropriate work within their 

spied limits. Even when different structures are inter- 
mingled, as when tendon and muscle mingle together at 

p place of union, there is no confusion in the work of the 
two sets of la borers. 

191. Concert of Action shown in Producing 
different Shapes. — The concert of action which we 

in the different sets of formative vessels is to be 

looked al from another point of view. It is such thai they 

a definite and peculiar shape to the structure which 

they make. Each bone differs in shape from every other 



15G PHYSIOLOGY AND HYGIENE. 

bone, each muscle from every other muscle ; and so of other 
parts. There is very great variety of shape in the structures 
of the body ; and each shape can be determined only by a 
certain concert among the builders, 

This concert of action may be looked at from still another 
point of view. In the growth, that is, the construction of 
any part, the addition is made by the formative vessels at 
every point of the part, and not upon the outside merely. 
As these builders are at work enlarging the part in the 
growth from infancy to childhood, they must so act in con- 
cert as to preserve the same general form in the part during 
all the successive stages of growth. And, as all the different 
structures of the body enlarge together, there must be agree- 
ment between different sets ; else there would be encroach- 
ment and confusion. 

192. Change of Action. — But this concert of action 
appears the most wonderful when a new action, or change of 
action, is called for. In the transition from childhood to 
youth, for example, the builders of the apparatus of the voice, 
the larynx, all at once become unusually active in their work, 
and a great enlargement of this musical instrument, for such 
it is, takes place, so that it may now utter the grave notes 
of manhood. 

Soon, too, the beard-builders begin their new work upon 
the face. And during the period of childhood new opera- 
tions have been continually instituted among the builders 
of the teeth, as one tooth after another has made its appear- 
ance, and as the new set have replaced the old. 

To effect each one of these changes, there must be con- 
cert of action among the formative vessels ; and there must 
be a most wonderful concert among the different successive 
sets of builders, to make all these series of operations work 
out at length the general result. 

193. Tadpole and Frog.— This change of action in 
the formative vessels is strikingly exemplified in some ani- 
mals. We refer to those that entirely change their forms 
during the period of their existence. One example will bG 
given ; the common frog. He is at first what is termed a 






FORMATION AND REPAIR. 



L57 



tadpole, and goes through many successive changes to become 
a complete frog. These changes are represented in the 

wing figures. The relative sizes are not preserved, the 
tadpole state being represented relatively much too large, for 

purpose of showing more clearly the development of the 

The young tadpole is represented in Fig. 91. It has 

a large head and body, and a long flat tail by which it swims 

y. There are no prominences to indicate the putting 
forth of any thing like limbs. It has gills, in the form of 
loose fringes on each side of the head. 

Fig. 02. 



Fig. 91. 





These gills after a time disappear, and it has another set 

of gills arranged under a fold of skin very much like the 

gills of a fish. The form is then as in Fig. 92. The next 

change is this. The hind legs begin to grow out as seen in 

Next, the four legsap}> on in Fig. 94. 'Hi' 1 

still v.-ry large. This now gradually disappears while 

as represented in Pig. 95. 

In '. repree the perfect frog, the tail I 

entirely disappeared. With these exterior changes interior 

ones have been going on also. The animal, which was at 



158 PHYSIOLOGY AND HYGIENE. 

first like a real fish, breathing with gills and swimming in 
water, has lost its gills, and has now a pair of lungs ; and it 
is no longer able to remain long under water, but must 
come to the surface to breathe the air. 

194. Change of Action to meet new 'Exi- 
gencies. — The change of action in the formative vessels, 
which is sometimes called for by accident and disease, 
exhibits in an interesting manner the concert between 
these vessels as influenced by circumstances. When a bone 
is broken, these formative vessels set themselves at work to 
repair the injury, by forming new bone between and around 
the two ends of bone, which new bone w r e call callus. 

195* Illustration from Processes of Inflam- 
mation. — Concert of action under successive changes is 
strikingly exhibited in the processes of inflammation. The 
following account of these processes is from a work pub- 
lished by the author, entitled " Physician and Patient." 
" You see a swelling. It after a while begins to soften. 
There is matter in it, but it is not yet very near the sur- 
face. But soon, at some point, it comes nearer and nearer 
to the surface, the wall of the abscess thus becoming con- 
stantly more thin, till, at length, it opens and discharges. 
The discharge continues till the swelling is nearly all gone, 
and the remainder is absorbed, and the part is restored 
to its natural state. 

" Just look for a moment at the complicated character of 
this apparently simple operation. Here is quite a large 
deposition of substance which is to be removed ; and this 
is the object to be effected. Observe how it is done. The 
softening of the swelling is not a mere change of solid sub- 
stances into a fluid, as if by decay, but it is the result of an 
active process, which we call suppuration. When this pro- 
cess is properly performed good pus is made, or as the old 
writers in medicine rather quaintly expressed it, laudable pus. 

" This process of suppuration, when it is well done, does 
not go on here and there in the swelling, making it like 
a honeycomb with a multitude of little abscesses ; but there 
is a concert, an agreement of action by the vessels of the 



FORMATION AXD REPAIR, 159 

. as really as if they worked intelligently. It is this 
concert of action which not only makes the Hue of move- 
ment in the abscess, but points it towards the surface, 
instead of giving it some other direction, laterally or 
inward, upon some of the internal organs. 

••Three different offices are performed by the vessels in 
the different quarters of the abscess. While some of these 
little workmen are forming the pus, there are others thin- 
ning the wall of the abscess in the direction of the surface, 
by absorbing or taking up the substance there; while there 
are others still, in the rear, and at the sides of the abscess, 
depositing substance, in order to make a barrier to prevent 
the pus from being diffused in the surrounding parts. 

" When the absorbents have completed their passage for 
the pus through the skin, the pus is gradually discharged 
from its reservoir, and the k ' occupation ? of the pus-makers 
>on ' gone.' The wall-builders also cease their work, 
and while the vacancy becomes filled up by contraction and 
deposition, the wall of defense, so carefully maintained so 
long as needed, is now taken up by the absorbents — work- 
men which seem to know just when, as well as how, to do 
their duty." 

196. Formation of all Parts from the Blood. 
— Thus, all the solids and fluids in the body are made from 
the blood. Even the heart itself is made from the blood 
which it pumps into the aorta; for from this aorta go out 
small arteries, to carry blood to the walls of the heart for 
growth and repair. 

1UH . Waste. — Not only is there construction going on 

in every part of the system, but there is waste also. The 

wear and tear of the eyer-moving machinery continually 

make- some of the particles useless, and these musl in 

way be removed. Lei U9 BG6 how this is done. 

198* Ttro Kinds of Waste Matter. — There are 

kind- of waste particles; and for the disposal of them 

pursued. Some of t he waste parti- 

. though wholly where they are. can be rendered 

fit to be used again by being subjected to certain proce- 



1(30 PHYSIOLOGY AND HYGIENE. 

These, therefore, are not thrown out of the system, but 
are taken up by absorbents, and are carried where the 
necessary processes can be applied to them ; and then they 
are introduced into the blood ; to make again a part of the 
building material. 

But there are some waste particles that cannot be used 
again ; and these are so managed as to be got rid of at 
various outlets of the system. These two kinds of particles 
are taken up by two different sets of absorbents. The 
selecting power which they thus exert is as unerring as if 
they were possessed of intelligence. 

199. Lymphatics. — The particles which can be 
used again are taken up by absorbents, which are termed 
lymphatics. These vessels are much like the lacteals, the 
absorbents in the intestines. They unite together, as they 
come from all parts of the body, into two trunks. One of 
these is the thoracic duct, which is the common duct both 
of the lymphatics and the lacteals (Fig. 6), and in which 
the chyle and the lymph, as the fluid in the lymphatics is 
called, are mingled together. 

The other trunk, which receives the lymph from but a 
small part of the body, empties its contents into a large 
vein at the right side of the top of the chest. The largest 
part of the lymph, therefore, unites with the chyle, and is 
poured with it into the circulation, and the rest reaches 
the same destination by another way. It all becomes with 
the chyle a part of the blood. But before this it passes, 
like the chyle, through glands, in order to fit it to become 
again a part of the building-material of the body. These 
glands are everywhere in the track of the lymphatics. 
They are often enlarged from disease, and then they can be 
readily felt. In relation to this appropriation of waste par- 
ticles, it may be truly said that man lives in part upon 
his own flesh. 

Those waste particles which are entirely useless are taken 
up by the veins directly into the circulation. They then 
travel the rounds with the blood, and are thrown off from 
the system by organs fitted for that purpose. These organs 



FORMATION AND REPAIR, 1G1 

are the lungs, the skin, the liver, the kidneys, etc. Each 
of these excretory organs is fitted to throw off its particular 
part of the waste. Thus the lungs excrete a kind different 
from that which the skin does; and so of the rest. 

200. Excretion and Secretion.— It is interesting 
to observe that some of the excretory organs perform other 
functions besides that of mere excretion.* Thus the lungs, 
while they excrete carbon, absorb oxygen, without which 
life could not go on. At the same time, too, they act as the 
bellows for the organ of the voice, the larynx, as you will 
see in the chapter on that subject. So, also, the liver, while 
it excretes what would be noxious if it remained in the 
blood, puts its excretion into such a form, that it proves, as 
you saw in the chapter on digestion, an auxiliary in some 
of the processes of the digestive organs. 

201. The Shin. — The skin, while it is an extensive 
excreting organ, performs other important offices. It serves 
as a firm yet very flexible and soft covering to the body, 
protecting its internal parts from injury. It is highly en- 
dowed with nerves for two purposes — the one, that it may 
act as a sentinel to warn of danger; and the other, that it 
may be the seat of the sense of touch. What is very com- 
m nly spoken of as the skin, is not really the skin, but only 
I covering for it. 

202. Cuticle. — When the skin is rubbed off, as it is ex- 
pressed, it is only this covering of the skin, or cuticle, which 
is removed. The skin which is raised by a blister is this 
cuticle. The great object of the cuticle is to protect the 
true skin, which is very fully supplied with nerves for 
the purposes mentioned above, and which therefore, if un- 

Bred, would prove a Bource of severe suffering. As it is. 

•Thew return, xre often applied to the Bame 

tiling. Excretion, strictly speaking, should be applied <>nly to some- 

j to be thrown off t and not to something formed to be used. Hut 

Times an excretion is so formed that it can !><• used, and then the 

word is also applicable to it. Thus the bile, while it Is an 

excretion containing noxious particles to be thrown off from the system, 

, and BO it is as often railed a secretion as an < xnvtion 



102 



PHYSIOLOGY AND HYGIENE. 



Fig. 97. 



the cuticle protects the skin effectually, and yet does not 
interfere with its functions as the organ of the sense of touch. 
It is of so slight and so soft a texture, that the nerves of 
touch may readily receive impressions through it. It is 
composed of many layers of minute round cells, the outer- 
most layers being made up of these 
cells broken and emptied of the 
fluid which they contained. 

203. True Skin.— The true 
skin, which the cuticle covers, is of 
a fibrous texture, with a good supply 
of both nerves and blood-vessels. 
On the surface of this true skin 
next to the cuticle are eminences 
called papillre. In these are seated 
the extremities of the nerves of 
touch. Fig. 97 represents a highly 
magnified section of a bit of the 
skin from the sole of the foot ; a is 
the cuticle ; c is the true skin ; b 
represents the papillae. 

204. Tailing in the Shin. — 
You observe a tube which runs 

up through the cutis or true skin 
and the cuticle, and in the latter 
takes a spiral course. This is the 
discharging tube of the sweat-gland, 
d, lying within the true skin, and 
surrounded with globules of fat. 
These glands are more numerous 
in some parts of the skin than in 
others. They are particularly nu- 
merous on the palms of the hands, 
and on the soles of the feet. 

Mr. E. Wilson counted, with the 
aid of the microscope, 3528 of them 
in a square inch on the palm of the 
hand. Beckoning the length of 




Vertical secfion of the 
SOLE OF THE FOOT. 



FORMATION" AND REPAIRS. 



LC3 



one of those at one quarter of an inch, it gives 882 inelies 
or 73J feet of tubing in this small space. lie calculated the 
amount of this tubing in the skin of the whole body as 
being 48.600 yards, or nearly '-28 miles. The amounl 
excretion from the seven millions of these tubes, which 
open on the surface of the skin, is very great. 

205* Insensible Perspirati<on. — The perspiration 
is ordinarily insensible, as it is termed; thai is, it is in the 
form of vapor. But sometimes, as in vigorous exercise, 
when the sweat-glands are rendered very active, chiefly to 
prevent too great an accumulation of heat, the perspiration 
becomes sensible. 

206. Sebaceous Glands. — There is another set of 
glands in the skin, called sebaceous glands, which secrete 
on oily fluid. They also have thin tubes like the sweat- 
glands. They are most abundant where the skin specially 
needs an oily lubrication, as where there are folds in the 
skin, or hairs, or where the skin is ex- 
posed to friction, or to the drying at- 

,'here. They are very abundant on 
the face and head. Every hair has se- 

hjus glands connected with it, as rep- 
resented in Fig. 98 ; in which b is the 
hair emerging from the skin ; a a are 
the sebaceous glands pouring their se- 
cretion by thin tubes into the tube or 
canal in which the hair grows ; c the 
root of the hair surrounded with fat 
globules. 

207. Influence of labor on 
Wear and Tear, and on Absorp- 
tion — By the Eactfl developed in this 
chapter, it is thns scon thai there is con- 
change going <>n in all parts of the 

Particle- which have bee 

ire taken up by the absorl i 
while the format i deposil 

others to take their places. The rapidity with which this 




c 

and sebaceum 



104 PHYSIOLOGY AKD HYGIENE. 

change occurs, depends mostly upon the activity of the 
individual. The busy laborer, whether the labor be bodily 
or mental, requires more nourishment than the indolent 
man, because there is more waste in his case, from the wear 
and tear occasioned by motion or thought, and there is 
therefore a necessity for a larger supply of repairing material. 

The difference, it is true, is not so great in regard to 
mental labor, as in regard to that of the body ; but still it 
is very apparent. This dependence of the amount of 
change in the system upon the degree of activity is very 
manifest, if we compare different animals in this respect. 
The frog and the canary bird, in regard to respiration, have 
been already contrasted, and they can be contrasted in this 
respect also. As the frog makes but little exertion either 
of body or mind, there is but little change in his body, and 
but little nutriment is required to supply the small waste 
that occurs. But in the ever active canary there is much 
waste from this action, and therefore there must be much 
eating to supply the material of repair. 

208. Change Varies in Different Parts of 
the Body, and in the same Body at Differ cut 
Times* — The relation thus seen to exist between the 
amount of change and the degree of activity, is exempli- 
fied in a comparison between different parts of the body. 
In those which are most actively used the change of decay 
and repair is going on most constantly. The active mus- 
cles and nerves are continually changing ; while the bones, 
which are only passive instruments of motion, are changed 
very slowly. 

And it is a significant fact, that in the case of the mus- 
cles and nerves, the waste particles are to a large extent of 
the entirely useless hind, for they are mostly absorbed by the 
veins, these tissues containing but few 'lymphatics. That 
is, whenever Ave think, or feel, or move, we render entirely 
useless quantities of the particles which make up the struc- 
ture of the muscular and nervous systems, and these are 
got rid of at the proper outlets, while other particles imme- 
diately take their places. 



CELL-LIFE. 105- 

'209. Life a Result of Death.— In this constant 
change going on in the body, life and death may be said to 
be brought into very near companionship. Every act of 
the mind, and every movement of the body, breaks down 
some of the structure; and the particles, which are no 
longer fitted to maintain the living functions, must he 
taken away as refuse dead matter, and new particles 
endowed with vital affinities must take their place. 

Action, destruction, repair, are the successive events 
which are ever occurring in every part of our frame. Ac- 
tion is followed by destruction, and in proportion to its 
intensity : and repair is necessary to lit it for further action. 
And so through life the nutritive functions are thus strug- 
gling against the tendency to decay and death, till at length 
at the appointed limit the struggle is given over, the vital 
affinities release their hold, and the common laws of dead 
matter take possession of the body. 



CHAPTER XI. 

CELL-LIFE. 

?/0. The Formative Vessels shown by the 
microscope to be Cells. — It is found by the aid of the 

microscope, that all the minute operations of the system 
performed by the agency of cells. They are not such 
- as are found in the cellular tissue, which arc mere 

interstices, communicating together, but they are bladders 

or sac-, and are filled either with a fluid alone, or with a fluid 
taining some grains of solid Bubstance, termed mole- 

eules. The usual form of the cell when il first appears ifl 

globular or spheroidal It is seldom, however, Been in this 

form ; for, besides the change of form from the pressure of 



166 



PHYSIOLOGY AND HYGIENE. 



neighboring cells, the cells themselves often assume various 
shapes from other causes. 

211. Seen in the Blood and in most other 
Parts. — Cells can be seen in the blood. If the web of the 
foot of alive frog be placed under the microscope, they 
may be seen sweeping along in the blood-vessels, like so 
many little bladders, varying their shape, according as they 
press on each other, or on the sides of the vessel. This is 
very well represented in Fig. 99, in which a portion of the 
web of a frog's foot is seen as magnified 110 diameters, 
The dark irregular spots which you see, as at 3, 3, are pig- 
ment cells, which give the color to the part. 

Fig. 99. 




CAPILLARIES IN THE WEB OF A FROG'S FOOT. 



Cells may be seen, not only in the blood, but also in most of 
the other fluids, as well as in the solids. The solid parts of ani- 
mal bodies are composed either of cells, or of structures pro- 



CELL-LIFE. 



167 



Fig. 100. 



duced by cells, 01 of a mixture of these structures with cells. 
s ii3 can b9 s lid also of plants. Cells, therefore, are the 
real formative vessels in both classes of organized beings. 

212. Cells in the Lower Animals. — 

have very striking exhibitions of the cells in 
the lower orders of animals. The Hydra, a repre- 
sentation of which is given in Fig. 1, seems to be 
made up of little else than cells. If you observe 
under the microscope one of its arms, as it moves 
about, the motion appears to be a motion of the 
cells upon each other. There are no fibres to be 
seen, to which the motion can be attributed. 
Fig. 100 represents one of these arms highly mag- 
nified. The cells, as you see, have somewhat of 
a spiral arrangement. 

213. Character and Color of Tissues 
dependent on the Contents of Cells.— 
The character of many of the tissues in the body 
depends on the contents of the cells. The cell 
itself, or the cell-wall, as it is termed, is con- 
sidered to be always the same. But the contents 
vary, and this variation makes generally the 
variation in the character, and in the color also, 
of the various textures. 

For example, all the glands are constructed essentially on 
the same plan ; and their difference depends upon the con- 
tents of the cells in them. Thus the liver differs from the 
tear-gland, chiefly because the former has cells which fill 
themselves from the blood with the components of bile, 
while the other has cells which fill themselves with the 
mtfl of the tears. 

The color of various parts, as the iris of the eye, the skin 
of the dark-colored, the hair, &c, depends upon a coloring 
matter which constitutes either a part or the whole of the 
c intents of particular cells. 

? 14. Selecting Power of the (ells. — It is clear, 

from th ffrhich have been stated, that the cells have a 

ting power. In the body they take from the common 



CELLS 

in the arm of 
the Hvdra. 



168 PHYSIOLOGY ASTD HYGIENE. 






pabulum or material, the blood, such constituents or sub- 
stances as they need for their particular purposes. Illus- 
trations of this have already been given, in speaking of the 
difference in the glands. Every cell contains its own pecu- 
liar constituents, which it has taken from the blood. For 
example, there are fat-cells which receive fatty matter from 
the blood, rejecting everything else ; pigmentary cells receiv- 
ing nothing but coloring matter from the blood, &c. The 
same thing appears too in plants. There are cells which 
receive from the sap volatile oil ; others, fixed oil ; others, 
starch ; others, coloring matter, &c. 

Fluids, and sometimes gases, enter the cells continually. 
The pores through which they enter are not visible even 
through the microscope, but of course such pores must exist. 
Their entrance is controlled by the selecting power to which 
allusion has been made. 

215. Cells Ileal Laboratories. — Not only is there 
a selecting power in the cell, but there is often a convert- 
ing power, by which new compounds are formed from the 
constituents introduced into it. The cell in this case, 
though so small as to be seen only by a microscope of 
considerable power, is a real laboratory, effecting chemical 
changes in its contents. There can often be seen quite a 
brisk movement in the molecules in the cell while these 
changes are going on. 

216. Different Offices of Cells.— Cells, as has been 
already stated, do not all perform the same office, but there 
are cells for a great variety of purposes. 

There are different kinds of cells in the blood. There are 
colored and colorless ones. The office of the colorless ones 
has not yet been satisfactorily determined. But we know 
more about the colored ones. These give the red color to 
the blood. They are not red when looked at singly, but are 
of a yellow cast ; and the red color appears only when 
several are together. 

217. Office of Bed Cells in the Blood— One 
office of these colored cells is to carry oxygen to all parts of 
the system, and return the carbonic acid to the lungs to be 



CELL-LTFE. 109 

thrown off. By carrying these cargoes back and forth in 
the circulation, these little cells perform a very important 
office. A very valuable part of the cargo of these cells is 
iron. In low states of the system, when the red cells are 
deficient, the administration of iron in some form is often 
found to be very effectual, in connection with a good diet, 
in remedying the deficiency. 

The proportion of these red cells varies mnch in different 
animals. It is largest in those which are the most active. 
The proportion is greater generally in birds than in the 
mammalia, and it is much greater in the latter than in rep- 
tiles or fishes. In man it varies much in different individ- 
uals. These cells are abundant in the ruddy, strong, and 
active ; while they are less numerous in the inactive, pale, 
and feeble. 

218. Manner in which Absorption is Per- 
formed by Cells. — There are cells for absorption, and 
cells for secretion and excretion. It has been said in the 
chapter on Digestion, that the vessels called lacteals absorb 
chyle from the contents of the intestine. It was formerly 
supposed that they did this through their open mouths on 
the surface of the mucous membrane. But the absorption 
is accomplished by cells, which are developed for this pur- 
pose at the extremities of the lacteals. They take up the 
chyle and discharge it into the lacteals, and they are dis- 
solved away in the very act of emptying themselves. 

A new crop therefore of cells appears every time the pro- 
cess of absorption is to be performed. And, what is still 
more curious, every time that absorption is to take place, 
there is cast off, as a preparatory step, a sort of pavement 
of cells from over every point in the mucous membrane 
where there is an extremity of a lacteal. The absorbing cells 
are thus uncovered, BO that they can perform their duty. 
1 this can be made clear by the following diagram. The 
surface of the mucous membrane of the intestine is not a 
perfectly smooth surface, but examined by a microscope, it 
en to be covered with eminences and depressions. Ab- 
ption takes place on the eminences, while the depressions 
8 



170 



PHYSIOLOGY AND HYGIENE. 



are the seats of secretion. In the diagram, Fig. 101, you 
have a representation of the arrangement of one of the 
eminences highly magnified. A represents it as it is in the 
intervals of digestion when absorption is not going on, and 



Fig. 101. 




DIAGRAM SHOWING ABSORPTION IN A MUCOUS MEMBRANE. 



B as it is during absorption ; a a are the absorbent vessels 
or lacteals ; b i basement membrane, as it is termed, an 
exceedingly thin membrane acting as a basement to the 
pavement cells c c ; d d the absorbing cells. When absorp- 
tion is not going on, the prominence is somewhat shrunken, 
and the pavement cells cover it. There are some granules 
or small grains, d, in A, which are, it is supposed, the germs 
of the absorbing cells, which you see developed in B. When 
absorption is taking place the prominence is swelled out as 
represented, the lacteal vessels are full, and the absorbing 
cells appear at their extremities, while the pavement cells 
have been thrown off, so that the chyle may have free access 
to the absorbing cells through the pores or interstices of the 
basement membrane. 

219. Manner in which Secretion is Effected 
by them. — While absorption thus goes on in the emi- 
nences, secretion takes place in the depressions. The dia- 
gram, Fig. 102, represents one of these depressions, or folli- 
cles, as they are termed, in two opposite states, when secret- 
ing, and when not secreting. In A, secretion is not going 



CELL-LIFE. 



171 



on, and the cells c, in the follicle, remain quiet. In B, on 
the other hand, secretion is taking place, and it is done by 
the casting off of cells, as represented. These cells dis- 
charge their fluid contents into the cavity of the intestine, 
and disappear, while other cells take their places. These 





DIAGRAM SHOWING SECRETION IN A MUCOUS MEMBRANE. 

follicles are really little glands. And the various glands, 
the salivary glands, the liver, the pancreas, &c, are made up 
essentially of such follicles arranged in different ways. 

220. Muscles made up of Cells. — There are some 
cells which are devoted entirely to the production of motion, 
for an ordinary muscle is composed of great numbers of 
chains of cells included in sheaths bound together. A 
muscle appears to the naked eye to be made up of fibres. 
Each one of these fibres is found by the microscope to be 
composed of from 500 to 800 fibrillm, or minute fibres. And 

Fio. 103. 




FIBRE OF A MUSCLE. 



each of these fibrillaa is a series or chain of cells. In Fig. 
103, a, is represented a fibre as seen under the microscope, 
showing the fibrillar of which it is composed. They are 



172 



PHYSIOLOGY AND HYGIENE. 



Fig. 104. 



separated at the broken end by the violence in tearing the 

fibre. In #, you see one of the fibrillae very highly magni- 
fied, showing that it is a chain of cells. In 
the diagram, Fig. 104, is represented the con- 
dition of a fibrilla in the two states of con- 
traction and relaxation. In a it is relaxed- 
In b it is contracted, the cells being short- 
ened, and at the same time widened. And 
as all the cells in the muscle are thus widened 
when the muscle contracts, we see the cause 
of the well known swelling out of muscles 
when they are in action. That you may form 
some idea of the size of these cells in mus- 
cles, I will state that in the space of the 
square of a tenth part of an inch, thus, □ , 
there are over 100,000 of these cells. 

221. Hoofs, Horns, Nails, and 
Teeth made by Cells. — There are cells 
whose office is to make certain solid deposits. 
Hoofs, horns, nails, and teeth are made in 
relaxed ; b contracted, this way. Even the hard enamel of the 
teeth is constructed by cells. They deposit 

it in the form of prisms of hexagonal shape as seen in Fig. 

105, which represents a vertical section of enamel as seen 

Fig. 105. 



h 

m 

M 

m 
m 
■ 
■ 
■ 
■ 
■ 




a 

1 

1 
1 
1 
1 
1 
1 
1 



MUSCULAR FIBRIL : 




VEETICAL SECTION OF ENAMEL. 



under the microscope. Their shape is more plainly seen 
in A, Fig. 106, which represents a transverse section of 






CELL-LIFE. 



173 



enamel. The line of these prisms is generally wavy, but 
they are for the most part parallel to each other. At B are 
Borne of these prisms separated. They are more magnified 
here than in Fig. 105. 

Fig. 106. 




ENAMEL. 

A, Transverse section. B, Separated prisms of it. 

222. Nerves composed of Tabes made from 

Cells. — The nerves are bundles of tubes of exceeding 
fineness. They vary from 16 1 00 th to to,Vo o^ 1 °f an i nc h in 
diameter. Now, each of these little tubes, or tubuli, as 
they are called, was once a chain of cells. The cells in 
each chain or row, as the microscope has shown, gradually 
became incorporated together to become a tube, and in this 
tube is contained the true nervous matter. 

And it is supposed that each of these tubuli preserves 
itself separate and distinct, from its origin in the brain, or 
some other of the central organs 
of the nervous system, to its 
termination in some fibre, or -A 
on .some surface. Fur no com- Q 
munications between the tubuli 
ever been found by any 
•pist. The manner in 
which these tubuli are made O 

i cellfl may be illustrated by 
the diagram in Pig. 107, in which the steps by which the 
row ol cells A becomes the tube B are represented, 

223* All Organized Substances built up by 
Cells. — All animated nature is built up by cells. 'Flic first 



Fig. 107. 



174 PHYSIOLOGY AND HYGIENE. 

thing which comes from the supposed germ is a cell. And 
this single cell is the parent of all the cells which build up 
the whole structure, whatever it be. It is by these cells thus 
produced, that all plants and animals are constructed. "A 
globular mass/' says Carpenter, " containing a large number 
of cells is formed before any diversity of parts shows itself ; 
and it is by the subsequent development, from this mass, of 
different sets of cells, of which some are changed into 
cartilage, others into nerve, others into muscle, others into 
vessels, and so on, that the several parts of the body are 
ultimately formed." 

224. Arrangement of the Parts of the JEf/fj. — 
By an examination of different eggs at different stages of 
the process of hatching, the various steps in the develop- 
ment of the animal have been observed and noted. In the 
middle of the egg is the yellow yolk, composed of albumen 
and oil globules. It is surrounded by an exceedingly thin 
sac, which keeps it separate from the albumen, or white of 
the egg that envelopes it. The yolk b, Fig. 108, is lighter 

Fig. 108. 




SECTION OF A BIRD'S EGG. 



than the white, and it therefore always seeks the highest 
point in the egg. But it is held down by two very delicate 
ligaments e, e, connecting it with the white lining of the 
shell. And you will observe, too, that the cicatricula, or 



CELL-LIFE. 



175 



germ-spot, a. which is a collection of cells beginning the 
process which is to form the animal, being lighter than the 
volk is always at the top of it, in order to receive the 
warmth from the body of the bird as it sets upon its eggs. 
There is at the blunt end of the egg,/, a bubble of air 
which is intended as an invigorating draught for the lungs 
of the young bird preparatory to its bursting its shell. 

225. Succession of Cells in the Yolk before 
the Animal is formed* — When the processes prepara- 
tory to the formation of the animal commence, the yolk 
itself is composed in part of cells, as represented in Fig. 109, 
A. In the midst of it there is a germinal spot, a, with a 
vesicle in it, b. This vesicle produces a cluster of cells. 




DEVELOPMENT OF CELLS IX THE YOLK DURING INCUBATION. 

But these cells, and those which in part compose the yolk 
are temporary, and all disappear. Before, however, the 
cluster of cells in the germinal spot disappear, there are 
. in the midst of them two twin cells. These multiply; 
and what is singular, they do it by doubling, so that there 
are successively 1, 8, 16, 32, &c. At length there La a mass 
of them like a mulberry, as at e, in B. This mass then 



176 PHYSIOLOGY AND HYGIENE. 

sends off cells at its edges which makes a layer, /, all round 
the yolk as represented in C. A second layer, g, is formed 
inside of the first as seen in D. In the case of the higher 
animals a third layer is added. 

226. Development of Organs. — There is no for- 
mation of the animal yet. Soon, however, a single large cell 
appears in the center of the mulberry-shaped mass of cells, 
and from this begins the formation of the animal. All the 
other parts of the egg — the cells, the yolk, the white — are 
tributary to the action which proceeds from this cell. 
Within its wall is a ring-like nucleus. This takes the shape 
of a pear, and then it is afterward very much like a violin. 
From this nucleus are produced cells which form all the 
various parts of the animal, the heart, lungs, stomach, 
brain, limbs, &c. And these are made of the yolk and the 
white of the egg. 

From the views which have been presented in this chap- 
ter it is manifest, that the grand distinction between organized 
and unorganized substances is to be found in this cell-life of 
the organized. In unorganized substances particles or mole- 
cules are the only things which we know of as being con- 
cerned in their formation. But in the construction of 
organized substances or beings, every thing is done by the 
agency of cells. And in this cell-life of the living world we 
have another beautiful example of the divers and almost 
numberless results which the Creator works out by simple 
and single means. 

As gravitation holds atoms together in masses of every size 
from the minutest to the largest, and keeps the mighty orbs 
in their appointed circuits, so cell-organization constructs 
and moves all living things, however small, however large, 
and however diversified. ^ 

227. The Power of the Deity shown in the 
Minute Operations of Nature. — As we examine 
the various workings of this cell-life, we can not but per- 
ceive the truth of the old adage, Natura in minimis 
maxima est — nature is greatest in the smallest things. The 
power of mere bulk or mere force we can comprehend by 



CELL-LIFE. ITT 

mental addition, however great that power may be. We can 
imagine a power which we see, to be indefinitely multiplied, 
and thus can form the idea of immense power. But 
when with the microscope we see minute cells working out 
such results as we have contemplated in this chapter, and 
inquire how it is done, we see that there is a hidden power 
here that utterly defies our conception. The mechanics and 
the chemistry of the cell, who can understand them ? 

From the inscrutable movements of this hidden power, at 
work wherever life is, in the cells, its laboratories, we get a 
higher idea of Omnipotence than we can get from the 
grandest and most terrific exhibitions of mere force. We get 
from them the idea of an all-pervading, as well as an all- 
wise power, working not merely in every locality, but at 
every point of the universe. And the revelations which the 
microscope makes to us seem to draw us very near to the 
Infinite. As we gaze with wonder and delight at the secret 
operations of his power thus opened to us, we seem almost 
to be admitted to his presence ; and even our awakened 
curiosity, amid the wonders now brought into our field of 
vision, does not suffice to remove the awe which almost 
oppresses us. 

How great is the inner beauty of the living w r orld around 
us! We admire the symmetrical forms, and the beautiful 
•rs which nature presents to us in such variety; but 
there is an inner world of beauties throughout nature, still 
more perfect and resplendent, which is hidden from the 
naked eye of man, though it is all open to the Omniscient. 

If you would get some idea of the beauty of this inner 
world, take the most delicately beautiful of all the specimens 
of man's workmanship, and examine it with a microscope; 
ihen compare it with some living texture or coloring. 
npare in this way, for example, the most perfect painting 
of a flower with the flower it-elf. The painting loses all its 
beauty as it is magnified; but in the bosom of the flower 
develops to you beauties far transcending 
iich arc seen by the unassisted eye. Even such liv- 
ing structures as are unattractive to the naked eye, pre- 



178 PHYSIOLOGY A^D HYGIEKE. 

under the microscope wonderful beauty in the delicate lines 
of their textures. 

It is true of every one who has used this instrument in 
his observation of nature, that he is impressed with the fact 
that, great as is the beauty of nature, as we lock out upon it, 
it is vastly inferior both in kind aiyl in amount to that 
inner beauty seen so completely by the all-seeing Eye, and 
now developed to us in part by the skill and ingenuity of 
man. And it suggests to us the hope, that in a new state 
of being, and with higher faculties, we shall be able to look 
farther into these inner beauties of the universe, than we 
now can with all the aids which our ingenuity can devise.* 



CHAPTER XII. 
THE NERVOUS SYSTE1J. 

228. Process of Nutrition in Plants and 
Animals quite alike* — Thus far we have contemplated 
man merely as a structure. We have observed the means 
by which the body is built and is kept in repair. We have 
seen that the functions of nutrition in man and all animals 
have much in common with those of plants. So far as 
these functions are concerned, they vary from plants only 
in the modes by which the nutrition is effected. 

The absorbents in the root of the plant do for the plant 
what the lacteals in the digestive organs do for the animal, 
the difference between them being only according to the 
differing circumstances. So also, circulation and formation 
are in all essential points the same in these two different 
departments of animated nature. 

* I could not find it in my heart to cut out the above paragraphs 
relating to the power of the Deity shown in the minute operations of 
nature ; though they contain little of direct instruction, the reading of 
them can not fail to make a good impression. — Ed. 



THE NERVOUS SYSTEM. 179 

229. The Nervous System — the Essential 
Difference between Plants and Animals. — The 

functions which have been treated in the previous chapters, 
as being common to plants and animals, are called the func- 
tions of organic life, because they concern merely the struc- 
ture, the organization. But there are other functions. The 
body, with all its complicated parts, is constructed and kept 
in repair for certain uses. 

These uses are secured by the nervous system, — a system 
which is superadded to what the animal has in common 
with the plant, and which, therefore, constitutes the essential 
difference between the animal and the plant. This system 
furnishes the means of the relations of the animal to the 
world around him. 

He receives his impressions from external things through 
this system ; and through it he acts upon external things. 
He feels through the nerves, and by the nerves excites those 
motions by which he acts on both material and immaterial 
existences. 

The functions, therefore, which are performed through 
this system, are called functions of animal life, in distinction 
from the functions of organic life, which are common to 
vegetables and animals. They are sometimes also called 
functions of relation, in view of the relations which it estab- 
lishes between sentient and moving beings, and all external 
things. 

230. Tlie Nervous System and its Subordi- 
nate Instruments. — The nerves do not themselves 
move, but they excite motion in muscles, and these move 
bones and other parts. Xeither is sensation performed by the 
nerves alone. The different senses, for example, have differ- 
ent organs, with arrangements differing according to the 
kind of sensation. Mere nerves alone do not sec, or hear, or 
taste, or smell, or touch. 

There are special organs constructed for these purposes ; 
and through these, the nerves receive impressions. Thus the 
nerve of sight can not of itself see; but the eye being there, 
so formed as to have pictured on a membrane the images of 



180 PHYSIOLOGY AND HYGIENE. 

objects, the nerve receives an impression from these images, 
and this impression is transmitted through the trunk of the 
nerve to the brain, where the mind takes cognizance of it; 
and this constitutes seeing. 

231. The Higher the Hank the more Compli- 
cated the Nervous System* — The nervous system in 
the lower orders of animals is very simple, and forms an ex- 
ceedingly small part of the animal. But, as we rise in the 
scale, we find that, as the limits of relation to external things 
enlarge, this system becomes more prominent ; till, in man, 
in whom these relations, both mental and physical, are 
much more extensive than in any other animal, it is very 
prominent and greatly complicated. 

232. All Knowledge Acquired and Commu- 
nicated hy Nerves. — A child as it first opens its eyes 
upon this world, knows nothing at the outset of shapes, or 
colors, or distances, or any other relations of things. This 
is all to be learned through the nerves and their subordinate 
organs. And as all knowledge is acquired through the 
nerves, so it is communicated through nerves to others. 

It is communicated by the motions that are excited in 
the muscles by the nerves ; by the motions of the countenance 
varying its expression; by the motions of the limbs, or 
gestures ; but especially by the motions which produce and 
articulate the voice. Thought and feeling can be communi- 
cated in no other way than by muscular motion. 

233. Parts of the Nervous System. — The nervous 
system may be considered as having three parts: 1, certain 
central parts, as the brain and spinal marrow ; 2, nervous 
trunks, which going from these central parts divide and sub- 
divide, as the arteries do, till they become exceedingly 
minute ; and 3, the nervous expansion in the organs, having 
a relation to the nervous trunks similar to that which the 
capillaries bear to the arteries. 

In what we call sensation we suppose that an impression 
is produced in the nervous expansion, that the trunk serves 
to transmit it, and that through the nervous center, the 
brain, it is communicated to the mind. 






THE NERVOUS SYSTEM. 181 

234* Condition? Necessary to Sensation and 
Motion. — Let us see now what is necessary to this com- 
pound act, termed sensation. First, it is necessary that 
the organ where the nerve is expanded be in a condition 
to let the nerve receive the impression. If the eye be so 
injured in its textures that the impression can not be made 
on the nerve, there can be no vision. 

It is necessary, also, that the trunk of the nerve be in a 
proper condition. If the nerve of vision be pressed upon 
by a tumor, there will be no impression transmitted from 
the images formed in the eye. So, too, if a nerve going to 
any part of the body be cut off, there can be no transmission 
of impressions to the brain from that part. 

Again, it is neeessnry to sensation that the brain should 
be in a state to communicate the impression to the mind. 
If the brain be pressed upon strongly by a depression of the 
skull from violence, or by effusion of blood by the rupture 
of an artery, as some times occurs in apoplexy, there can be 
no sensation. 

Excitement of mind, too, sometimes prevents the occur- 
rence of sensation, by its action upon the connection between 
the mind and the brain. The pain of a wound received in 
battle is often unfelt, until the excitement of the battle is 
over. The aching of a tooth is often stopped by the excite- 
ment consequent upon going to the dentist to have it ex- 
tracted. 

In these cases the cause of the pain is acting all the while 

upon the nervous extremity, and the trunk of the nerve is 

capable of transmitting the impression, but the state of the 

mind is such, and such is the consequent condition of the 

brain, that the sensation does not occur — one link in the 

.ssary chain is defective. The same can be said as 

irdfl the necessity of each of these links of the chain, in 

ion to voluntary motion, as well as to sensation. 

235. Genera/ Plan of the Nervous System* — 
In Fig. 110 there is presented a general view of this system, 
— the central organs witli the nerves going out from them. 
At a is the cerebrum, the upper large brain, filling up a con- 



182 



PHYSIOLOGY AND HYGIENE. 



Fig. 110. 




NERVOUS TRUNKS IN A MAN. 



THE NERVOUS SYSTEM. 



183 



siderable portion of the skull; at b is the cerebellum, the 

smaller brain, lying beneath the cerebrum at its back part: 

is the great facial nerve, the chief nerve of the face ; the 

spinal marrow, d, sends off branches on either side in its 

whole length ; at e is the brachial plexus, a bundle of nerves 

coming from the spinal marrow, which here unite together, 

and are then distributed to all parts of the arm; at lis a 

similar plexus from which are distributed nerves to the lower 

extremity ; /, g, and h point to different nerves in the arm, 

and /, ?/?, n, and o to different nerves in the leg. You observe 

that the wiiole of this nervous system is divided into exactly 

similar halves. The cerebrum and the cerebellum arc both 

double organs, and the nerves of one side are just like those 

of the other. 

Fig. ill 




h i k in 

BRAIN AND NERVES. 



236. Hemispheres <m<l Lobes of the Brain.— 
Having thus noticed the general arrangement of the nervous 

em, observe next the arrangement and structure of the 
brain which are seen in Fig. 111. This Figure presents to 



184 PHYSIOLOGY AND HYGIENE. 






view a perpendicular section of the brain, as made from front 
to rear, dividing it into two halves. You have here a view 
of the inner surface of one hemisphere, as it is termed, of the 
cerebrum, the large upper brain, which is commonly described 
as having three lobes or divisions : a, the anterior; h, the 
middle ; and c, the posterior. At / is the broad band of 
white fibrous matter, which unites the two halves or hemi- 
spheres, of course divided in the section ; at d is the cere- 
bellum, showing a peculiar arrangement, called the arbor 
vitce, or tree of life; at g is the beginning of the optic 
nerve which goes to the eye ; I is the olfactory nerve ; e is 
the commencement of the spinal marrow. 

237* Distribution of Nerves. — The many nerves 
which you see, are distributed to various parts of the face ; 
the nerve at li goes to the tongue ; at i, to the throat ; and 
at m. to one of the muscles of the eye. From the beginning 
of the spinal marrow go forth many nerves, one of which, 
k, is a very important one, as it sends off branches to the 
lungs, the heart, and the stomach. It is this part of the 
nervous system, the top of the spinal cord, that is most 
immediately essential to the continuance of life. For it 
is through their nervous connections with the top of the 
spinal marrow, that the heart and lungs continue to perform 
their duty. 

238. Functions of Respiration and Circu- 
lation depend on the Spinal Cord. — It has been 
ascertained, by experiments upon animals, that the cere- 
brum, and even the cerebellum, may be destroyed, and yet 
the animal will continue to breathe, and the circulation 
will go on for some time. But the moment that this part of 
the spinal cord is destroyed, from which the heart and lungs 
are supplied with nerves, the breathing and the circulation 
stop and the animal dies. So, too, in apoplexy, if the 
effusion of blood take place at the top of the spinal mar- 
row, death will occur, and in much shorter time, than if 
the effusion take place in the cerebrum or cerebellum. 

239. Cerebrum. — You observe that the cerebrum 
has deep irregular furrows on its surface, and that it pre- 



THE NERVOUS SYSTEM. 185 

Bents undulating tortuous projections. These are called 
the convolutions of the brain. Into the furrows between 
them dips down the membrane, in which branch out the 
arteries that supply the brain with blood, and the veins 
that return it from this organ. 

This membrane is, from its soft and delicate texture, 
called the pia mater (soft mother), while the stout fibrous 
membrane which lies outside of this next to the bony 
covering is called the dura mater (or hard mother). The 
names are entirely inappropriate, for the latter serves as a 
protection to the brain, and the former is merely a vehicle 
or medium for the entrance of the blood-vessels into the 
brain. There is another membrane lying between these 
which is called the arachnoid membrane, because in its 
tenuity and delicacy it resembles the spider's web. It is 
one of the serous membranes, and it serves as a protecting 
envelope to the brain, and at the same time, by its serum, 
keeps this organ bedewed with moisture over its whole 
surface 

240. Gray and White Substances. — The substance 
of which the brain is composed is very soft, something like 
blanc-mange. It is the softest organ in the body. In color 
it is not uniform throughout. All around the white inner 
part of the brain there is a thick layer of gray substance. 
In Fig. 112 you have a horizontal section of the brain, 
.-bowing the proportions and arrangement of the gray and 
vhite substance.-. As the gray substance dips down, 
as you see in the figure, into all the furrows, its extent is 
greater than would at first view be supposed. In the mid- 
dle is represented the broad band connecting the two hemi- 
spheres of the brain. You observe in Fig. Ill and Pig. 112, 
that there is no apparent arrangement of the external parts 
the brain which would give countenance to the idea of 
the phrenologist in relation to its division into particular 
involutions, far from presenting any well- 
defined arrangement, are exceedingly irregular. 

ill. The Gray Substance made of Cells; 
the White, of Tabes. — The gray substance, which is 



186 



PHYSIOLOGY AND HYGIENE. 
Fig. 112. 




SECTION OF THE BRAIN. 

sometimes called the cortical (bark-like) substance, because 
it surrounds the white central part of the brain, is made up 
of cells, while the white part is composed of exceedingly 
minute tubes. These tubes are continued into the nerves, 
and as they hold the nervous matter, they constitute the 
medium of communication between the brain and all parts 
of the body. 

This function of communication is the sole function of 
the white nervous matter. In the brain this white matter 
is a mere collection of tubes, and these branching out in 
bundles form the nerves. These tubes are supposed to be 
entirely separate from each other, from their beginning in 
the brain to their termination in the various parts of the 
body, for the microscope has never discovered any union 
between them at any point. 



THE XERVOUS SYSTEM. 



187 



Fig. 113. 




The brain, then, is a great central organ of communica- 
tion, where innumerable minute tubes are brought together, 
each of which is connected with some one moving fibre, or 
ie one sensitive point in the body. Those which are 
connected with muscular fibres transmit impressions from 
the brain, and those which are connected with sensitive 
points transmit impressions to 
it. Of the size of these tubes 
you can judge by Fig. 113, 
which shows some of them as 
they appear magnified 350 diam- 
eters. 

242. Office of the Gray 
Matter. — The office of the 

f substance, it is quite well 
ascertained, is very different 
from that of the white substance, 
as the difference in its structure 
Would lead us to suppose. It is 
more intimately connected with 
the mental operations than the 
white substance. When, for example, motion is produced in 
obedience to the will, the impression producing the motion 
U transmitted through the white matter, but the cause of 
this impression does not act directly on this matter. The 
impression is caused by the action of the mind on the gray 
matter, and the white substance serves only to transmit it. 
The gray matter, therefore, has a more active agency than 
white in the production of the phenomena of the mind 
and the nervous system. It is the first link in the chain of 
connection between tin* spiritual and the physical in our 
nature. Bence, in examining the brains of animals, we find 
that the higher the intelligence is. the more abundant is the 
QCe; and it ifl especially abundant in man, in 
the large developmenl of the convolutions. 

243. The Gray Substance well supplied with 
Arterial Blood.- A due Bupply of arterial blood is abso- 
lutely essential to the vigorous performance of the functions 



NERVOUS TUBULI, 

Magnified 350 diameters. 



188 



PHYSIOLOGY AND HYGIENE. 



of the gray substance. If the supply be cut off in any way, 
as by the failure of the heart's action in fainting, insensi- 
bility and loss of the power of motion are the consequence. 
While the gray substance is on the outside of the brain, it is 
on the inside of the spinal marrow. 

244. Ganglions and Plexuses. — It is also on the 
inside of the little bodies called ganglions, scattered here 
and there, as depositories of nervous force — little brains, as 
we may term them. These ganglions are not merely a part 
of the apparatus of communication, as are the plexuses, 
which are mere combinations of nervous trunks, as seen 
in Fig. 115, t t being the trunks, which, after uniting with 
each other in various ways, again separate to go to their 
different destinations. 

Fig. 114. 







At g, in Fig. 114, is a ganglion into which the fibres,/, of 
the nerve, n, run. They then separate again into branches 
Z>. These ganglions produce nervous force, and therefore 
are composed like the brain in part of gray substance. The 
spinal marrow, too, produces as well as transmits, and so 
this substance forms a part of it. 

245. Changes in the Nerve Cells.— This gray 
substance, as it is in constant operation, is subject to much 



THE NERVOUS SYSTEM. 189 

wear and tear, as we may express it, and therefore the 
changes of repair are constantly going on in its structure. 
Hence the necessity for so large a supply of blood as is 
secured by the network of vessels, among which the cells 
peculiar to this substance are scattered. 

246. Termination of the Nervous Fibres.— 
The extremities of the fibres, or rather of the tubuli, (Fig. 
113) of the nerves terminate variously. The most common 
termination is in loops, as seen in Fig. 11G, which repre- 
sents the termination of the nerves as seen through the 
microscope in a thin perpendicular section of the skin of 

Fig. 116. 







:SERVES OF TOUCH IN THE SKIN OF THE THUMB. 

the thumb. The three eminences in this figure are those 
of the papilla:, as they are termed, which you can see, if 
you look at the ball of the thumb, are arranged in curvi- 
linear rows. In Fig. 11? you see this same loop-like arrange- 
ment of the nervous tubuli, as seen through the microscope, 
on the sensitive sac that lines the cavity of a tooth, the 
entrance for the nerves and blood-vessels of this sac being 
at the end of the root. 

247. Pacinian Corpuscles, their Office not 
knoirn. — One very singular termination of the nervous 
tubuli, is in what are called Pacinian corpuscles, after 
Pacini, the first microscopist that discovered them. They 
are found attached to the nerves in the hand and foot more 
often than any where else. Their structure, which is seen 
highly magnified in Fig. 118, A, is very curious. They are 



190 



PHYSIOLOGY AND HYGIENE. 



attached to the branches of the nerves, on which they clus- 
ter by little peduncles or stalks. At a is the peduncle ; b is 



Fig. 117. 



Fig. 118. 




NERVES IN A TOOTH. 



PACINIAN CORPUSCLES. 



the nervous fibre or tubulus ; / is its termination in the 
corpuscle. In B is represented a portion of a nerve of a 
finger, with clusters of these corpuscles of about the natural 
size. Of what use these singular bodies are we know not. 
It has been supposed by some that they are minute elec- 
trical batteries, because they bear some resemblance to the 
electrical organs found in some fishes. 

248. Healing of Nerves. — There is a wonderful 
fact in regard to the healing of wounded nerves which must 
not pass unnoticed. You know that if a nerve be divided, 
no impressions can be transmitted through it to and from 
the brain. But the two cut ends of the nerves can grow 
together, and the communication can thus be more or less 
restored. Sometimes it is perfect as before. Now, if you 






THE XERV0US SYSTEM. 191 

call to mind the structure of a nervous trunk, you will see 
that this is passing wonderful. It is made up, you will 
recollect, of tubuli which are entirely separate from each 
other, and each one of these goes, from its origin in the 
nervous center to its destination, by itself. It is difficult to 
conceive, therefore, how the nerve can be healed without 
creating confusion. 

249. Nice Fitting of the Tubuli.— For to avoid 
this, it would seem to be necessary that each little tube at 
its cut end must unite with its corresponding end, and not 
with the end of some tube with which it has no relation. 
For example, if the nerve distributed to the hand were cut, 
it would not do, as it seems to us, to have tubuli which go 
to the thumb unite with those which go to a finger. 

And besides, as it will soon be shown you that the tubuli, 
through which the impression that produces motion i3 
transmitted, are separate from those which transmit the 
impression that causes sensation, it would not do for a 
tubulus of one kind to unite in the healing with one of 
the other kind. 

That there is, however, a very accurate union effected, is 
manifest from the observations of M. Brown Sequard. 
He examined in animals nerves which were divided twelve 
months before, and could not discover the point of divi- 
sion even with the aid of the microscope. If the tubuli 
were not all made perfectly continuous as before the 
nerve was divided, the microscope would have revealed the 
defect. 

But it takes time to effect this adjustment of the tubuli, 
for it was found by Dr. Haighton that after dividing nerves, 
their functions were not restored till some time after they 
were apparently healed. 

250. New Nervous Connections Formed. — 
Taking this view of this interesting point, the difficulty is 
itlv enhanced, when we look at the union of parts that 
did not originally belong together, as, for example, when a 
piece of skin is dissected from the forehead, and is twisted 
down so as to be made to grow on to the nose to supply a 



192 PHYSIOLOGY AND HYGIENE. 

deficiency there. Here entirely new relations are estab- 
lished between the nerves of the divided parts, and, as we 
should expect, there is confusion in the sensations. The 
patient, at first, whenever the new part of his nose is 
touched, refers the sensation to the forehead. But this 
confusion of the sensations is after awhile removed. And 
it is curious to observe, that while the old nervous connec- 
tions are breaking up, aud the new ones are becoming 
established, there is an interval of partial, sometimes entire, 
insensibility in the part. How these new relations can be 
established consistently with the known arrangement of 
the tubuli in the nerves is a mystery. 

251. Nerves of the Spinal Marrow Com- 
pound. — The nerves through which the mind sends its 
messages to the muscles, are not the same as those through 
which it receives impressions in sensation. In and about 
the face, the nerves of motion and sensation are, for the 
most part, entirely separate from each other. But in other 
parts of the body, the fibres or tubuli for motion and sensa- 
tion are mingled together in the same nervous trunk, in- 
closed in one sheath. 

It is found that each of the nerves, coming out from each 

side of the spinal marrow, has two roots, which unite, 

Fig. 119. an ^ are inclosed in one sheath. This 

a arrangement is represented in Fig. 119, in 

which a is a portion of the spinal cord; 

Jk""" d the anterior root; b the posterior root; e 

l^L c the trunk formed by the union of these two 

Tp^ roots ; and/ a branch of the nerve. At c, 

; \-"o on "the posterior root is one of the ganglions, 
I , or little brains, previously mentioned. Why 

pinal cord *^ e y are P^ ace( ^ on these posterior roots, and 
not on the anterior, or why they are placed 
here at all, we know not. 

252. Different Nerves for Different Offices.— 

It has been ascertained by many experiments on animals, 
that the posterior roots are composed of tubuli, which bring 
impressions to the spinal marrow; while the anterior are 



THE NERVOUS SYSTEM. 193 

composed of tubuli which carry impressions from the spinal 
marrow. For. if the spinal cord of an animal be laid bare, 
and a posterior root be irritated, pain is produced; but 
if an anterior root be irritated, violent motions are caused 
in the parts to which the nerve is distributed. That is, 
the posterior root is a nerve of sensation, and the anterior 
a nerve of motion. It is a matter of convenience that 
they unite and are mingled together in the same sheath, 
for they are to be distributed in the same parts. In and 
about the face the nerves of motion and sensation are kept 
for the most part separate, as before stated, merely because 
it would be no convenience in any case to put them together 
in one sheath. 

253. Nerves of Special Sensation. — But not only 
are there different nerves for sensation and for motion, 
but there are also different nerves for different kinds of sen- 
sation. Thus, in the eye, the optic nerve which transmits 
the impressions from the images formed on the retina, as 
will be shown in the Chapter on the Eye, is wholly separate 
from the nerve by which any pain or irritation is felt in this 
organ. The latter is called a nerve of common sensation — 
the former a nerve of special sensation. So in the nose, 
the nerve that takes cognizance of odors is a different one 
from that by which irritation of the lining membrane is felt. 
The snuff-taker smells the snuff with one nerve, and feels 
tingling with another. 

Each set <»f nerves is fitted for its own peculiar office, and 
for this its own peculiar susceptibility. Thus, the nerves 
ouch are insensible to light, and, on the other hand, the 
nerves of vision are insensible to touch. If, therefore, the 
nerve of vision be paralyzed, but the nerve of common sen- 
11 in the eye be unimpaired, although there is no seeing, 
- - Qsible t<» irritation as ever. 
the other hand, if the nerve of vimon be unimpaired, 
and the [ common sensation be paralyzed, ae some- 

times happens, the individual can see, but ho has lofil the 
Del that stand- guard over the eye. and by its framing 
of pain keeps it from injury. What, therefore, is Hying in 



194 PHYSIOLOGY AND HYGIENE. 

the atmosphere may lodge in the eye, and though it pro- 
duce no pain, it will excite inflammation by irritating the 
capillaries. 

When the nerve of common sensation is in a healthy 
state, the moment any thing gets into the eye great pain is 
produced, and the tears flow and the eyelids are in constant 
motion ; and by these instinctive means, as we may term 
them, the irritating substance is removed. But when this 
nerve is paralyzed, although the irritating substance pro- 
duces no pain, it gradually causes inflammation in the deli- 
cate vascular texture of the eye. 

254. Different Degrees of Sensibility in the 
Various Parts of the Body. — Different parts of the 
body are endowed with different degrees of sensibility, ac- 
cording to their necessities, in relation to the warning of 
danger. Thus the skin is the most sensitive part or organ 
of the body, that it may warn at once of the approach of 
danger; while the internal parts have much less sensibility, 
and some of them have none. In the performance of opera- 
tions, therefore, the great suffering is in the cutting of the 
skin. There is very little sensibility in the muscles, and 
there is none in the bones. 

The following fact illustrates the use of the sensibility of 
the skin in the prevention of injury. A man who had lost 
all sensibility in his right hand, but retained the power of 
motion, lifted the cover of a pan when it was burning hot. 
Although he was not aware of any effect at the moment, 
the consequence was the loss of the skin of the fingers and 
of the palm of the hand, laying bare the muscles and 
tendons. 

255. Inflamed Parts very Sensitive. — Although 
there is so little sensibility in the internal parts in their 
healthy condition, yet when they become inflamed they 
become painful, sometimes acutely so. Thus, an in- 
flamed bone is the seat of severe pain; and the tendons, 
although nearly insensible ordinarily, become very painful 
when inflamed, as any one that has a deep-seated felon can 
testify. The question as to the cause of this change of 



THE NERVOUS SYSTEM. 195 

sensibility wo will not stop to discuss, but that there is a 
benevolent object in it is very manifest. If inflammation 
caused no pain in such parts, it might go on to a destructive 

ut without the person's being aware of the danger, and 
therefore without his applying for medical aid. 

250. Nerves not Sensitive. — It was formerly sup- 

d that a nerve must of course have an exquisite sensi- 
bility. But there is no sensibility in nerves devoted to 
motion. Neither is there any in the brain itself. Portions 
of it can be cut off without producing any pain. The heart, 

is insensible to the touch. A case proving this fell under 
the observation of Harvey, the discoverer of the circulation 
of the blood. This absence of sensibility in the heart is not 
because it is not well endowed with nerves. It is well 
endowed, but with nerves which are devoted to another 
purpose. They are nerves of sympathy, which establish a 
connection with every part of the body, making this organ 
to be so easily affected by motion, by disease, and by every 
passing emotion of the mind. 

257. Respiratory Nerve of the Face.— In the 
face we have an example of different sets of nerves for 
different classes of motions. All those motions that are 
used in the expressions of the countenance are associated 
by a certain nerve. Sometimes this nerve of expression is 
paralyzed on one side. The result is, that while the indi- 
vidual can masticate equally well on both sides, he can 
laugh, and cry, and frown, only on one side, and he can not 
close the eye on the side affected. 

258. Paralysis of the Respiratory Nerve of 
the Face. — In Fig. 120 is a representation of this condi- 
tion <»f things. The left eye cannot be closed by any effort, 
and the left side of the face is wholly devoid of expression. 

rve of expression is often paralyzed by itself, the 

other nerves in the neighborhood, both of sensation and 

of motion, being entirely unaffected. This has been 

the respiratory nerve of the face, because it con- 

liich arc connected with the movements 

of respiration. If you observe how the various passions and 



196 PHYSIOLOGY AND HYGIENE. 

emotions are expressed, you will see that there is a natural 
association between the muscles of the face and those of the 

Fig. 120. 




PABALYSIS OP THE NERVE OF EXPRESSION 

on one side of the face. 



chest in this expression. This is very obvious in laughing 
and in weeping. When the nerve of expression, or facial 
respiratory nerve, is paralyzed, all the motions of the face 
connected with the respiration are absent. 

Though the individual may sob in weeping, or send forth 
the rapid expirations of laughter, yet the face on the 
side where the nerve is paralyzed will be perfectly quies- 
cent. So, too, those movements of the nostrils which are 
sometimes used in expression, are rendered impossible. 



THE NERVOUS SYSTEM. 197 

Sneezing and sniffing up can not be done on the affected 
side. Neither can the individual whistle, because a branch 
of this nerve goes to the muscles ar the corner of the 
month. 

259. Nerves of the Eye. — The eye has six different 
nerves, each having its distinct office and its separate 

;n in the brain for a different service. 1. The optic 
nerve, whose sole office is to transmit impressions from 
the images formed in the eye to the brain. 2. A nerve of 

mon sensation, through which any irritation in the eye 
is felt. 3. A nerve which is distributed to the muscles of 
the eye generally, and to no other parts of this organ. 4. A 
nerve which goes only to one of the oblique muscles of the 
This is an involuntary muscle which performs the in- 
able rolling motions of the eyeball, and is associated with 
the muscles of expression in the countenance by means of 
nervous connections. 5. A nerve which goes to another 
single muscle, which turns the eye outward. 6. A branch 
of the respiratory nerve, which regulates the motion of the 
eyelids, and has much to do, therefore, with the expressions 
of the countenance. 

260. Paralysis affectum/ Different Nerves. — 
Attention has been incidentally called to the fact, that one 
nerve may be paralyzed, while others distributed to the 
same parts are entirely unaffected. So, too, in the nerves 
which go out from the spinal marrow, composed of tubuli 
of motion and sensation mingled together, one set of the 
tubuli may be affected while the other is not; for in par- 
sis it is often the case that sensibility remains while the 

•r of motion is gone, and vice versa. 

Sir Charles Bell relate- an interesting case, in which the 

in the two side- of the body. A 

her was seized with a paralysis, in consequence of which 

is a loss <>f muscular power on one side, and a Loss 

ibility on the other. - ould hold her child with 

the Bide which retained its power of motion but 

had lost its sensibility, but only when .-lie was looking 



198 " PHYSIOLOGY AND HYGIENE. 

at it. She could not feel her child on the arm, and there- 
fore when her attention was drawn to any thing else, and 
she ceased to have her eyes fixed on the child, the muscles 
having no overseer, as we may say, to keep them at work, 
were relaxed at once, and the child would fall from her 
arm. 

261. Nerves, though having Different Offices, 
all alike in Structure. — The microscope shows us 
that the nerves of motion and of common and special sen- 
sation are all alike in their structure, and chemistry shows 
us that they are alike also in their composition. The ques- 
tion arises, then, why the impression producing motion can 
not be transmitted by the same nerve with the impression 
causing sensation. The reason is evidently not to be found 
in the nervous trunk itself, as this is the same in all cases. 

It is in the circumstances of the two ends of the nerve — 
that which is in the nervous center whence it arises, and that 
which is expanded in some part of the body. The nervous 
tubuli which end in the fibres of a muscle can not transmit 
impression to the brain from the skin over the muscle, 
because they do not go to the skin at all. There are other 
tubuli that are distributed there for that purpose, mingled 
indeed in most cases with the tubuli for motion, but yet 
kept entirely distinct from them. 

And besides, there is probably something in the struc- 
ture of the extremities of a nerve of sensation, which 
differs from that of a nerve of motion, so as to make it 
impossible for a nerve of motion to receive the impression 
producing sensation, even where the impression is made 
directly upon the muscle itself. There is also probably a 
different ending of the nerves of sensation and motion 
in the nervous center, the brain, or spinal marrow, that 
makes the one kind incapable of performing the duties of 
the other kind. 

262. Products of Nervous Action.— We have 
thus far contemplated nervous action, for the most part, 
only in two forms — as producing either sensation or volun- 
tary motion. In sensation the action is from the extremity 



7 



THE NERVOUS SYSTEM. 199 

of the nerve to the nervous center ; but in motion it is 
from the center to the extremities of the nerves, as they 
are expanded among the fibres of the muscles. This volun- 
tary motion, you see, may arise in consequence of sensation, 
lien you withdraw the hand from the fire, if the heat 
be painful : or it may occur without a preceding sensation, 
as when the thinking mind wills to perform certain mo- 
tions for effecting some purpose. 

In either case it is supposed that the gray vesicular or 
cellular substance of the brain is in immediate connection 
with the mind, and that the white tubular matter of the 
brain and the nerves serves only for transmission. That 
is, both in sensation and in motion the effective physical 
agency is in the vesicular gray substance. This is the 
working part of the telegraphic apparatus of the mind, 
while the innumerable tubuli of the white matter of the 
brain and nerves are the communicating wires. 

263m Involuntary Action. — Much of the muscular 
motion of the body is produced without the agency of the 
will, and sometimes even in opposition to it. This is true 
of the motions caused by emotions in the mind. For ex- 
ample, the muscular motions in sobbing and in laughing 
often occur in opposition to the strong action of the will. 
In this case, the emotion produces its effect upon the gray 
vesicular substance, and is transmitted through the nerves 
to the muscles. 

There are some common motions which are performed 
to a greater or less extent without the agency of the will. 
The muscles which perform them are called involuntary 
muscles. The muscles of respiration, for example, ordina- 
rily act without our willing them to do so. If they did not, 
iration would stop when we sleep, or be stopped by 
But the will can quicken these muscles in their 
>n. They arc therefore not wholly involuntary. 

But there are some purely involuntary muscles. The 

- ular coat of the stomach, which was spoken of in the 

pter on Digestion, as being constantly in motion when 

the stomach is filled with food, is of this character. No 



200 PHYSIOLOGY AKD HYGIEKE. 

effort of the will can quicken or retard the action of this 
muscle. That exceedingly compound muscular engine, 
the heart, is a collection of purely involuntary muscles. 

264. Excitor and Motor Nerves. — We have already 
alluded to the two roots which unite to make up each nerve 
that comes from the spine. One of these roots is composed 
of tubuli through which impressions are transmitted to the 
spinal marrow ; and the other contains tubuli, through 
which an impression is transmitted from the spinal mar- 
row to the muscles, causing them to contract. Each nerve, 
then, coming from the spine, is made up of two distinct 
nerves, or two distinct sets of tubuli. One of these is called 
an excitor nerve, the other a motor nerve. 

In the case of the muscles of respiration, every time 
that they act, an impression is transmitted from the lungs 
through an excitor nerve to the spinal marrow, the gray 
vesicular substance there responding to this impression, 
and sending in consequence an impression by a motor nerve 
to the muscles. So, also, the presence of food in the 
stomach produces an impression which is transmitted 
through the excitor nerve, and another impression is re- 
turned through the motor nerve, exciting the muscular 
coat to action. And in the act of swallowing an impression 
is transmitted from the food thrust back into the throat 
and then impressions are returned to the many muscles 
engaged in this compound act. The action of the nerves 
illustrated by these examples is termed their reflex action, 
because the impression transmitted by one nerve to the 
spinal marrow is reflected from it by another. 

265. Sensation does not Accompany Nerv- 
ous Action. — In some cases the impression is accom- 
panied with actual sensation, and sometimes not, the 
action being confined to the spinal marrow. Thus, in 
the action of respiration, the impression carried from 
the lungs by the excitor nerves comes from the pres- 
ence of dark blood in the lungs. Ordinarily, a mere im- 
pression, and nothing like sensation, is transmitted. The 
respiratory muscles, most of the time, go on to do their 



THE NERVOUS SYSTEM. 201 

work, in obedience to the impressions communicated from 

the lungs, without any recognition of the process by the 

mind. 

But when there is embarrassment in the lungs, the quiet 

process, carried on through the agency of the spinal mar- 
row alone, is not adequate to meet the exigency. In some 
way, the brain becomes a party in the operation. The act 
of breathing is now accompanied with positive sensations, 
and there is a mixture of voluntary and involuntary mus- 
cular action. 

266. The Spinal Harrow Performs Two 
Separate Functions* — The spinal marrow, then, per- 
forms two separate functions — one, by itself, in pro- 
ducing involuntary motion ; and another, in connection 
with the brain, in producing voluntary motion and sen- 
sation. 

The arrangement by which it does two things which are 
so different from each other, will be clear to you, if you 
bear in mind the fact that the spinal marrowy like the 
brain, is composed of the two nervous substances, the white 
tubular, and the gray vesicular substance. 

When the spinal marrow acts as a mere medium of com- 
munication for the brain, the transmission is made directly 
through the tubes of the white substance to and from the 
brain — to the brain in sensation, and from it in voluntary 
motion. Tims, when a sensation is felt in the foot, the 
impression made there is transmitted through the nerve to 
the spinal marrow, and up through the white part of this 
!i to the brain. It touches none of the gray substance 
of the spinal marrow, but^goes to the gray substance of the 
brain. And when the foot is moved, an impression is re- 
turned from the brain through the white part of the spinal 
marrow, and then through the nerve which goes from it to 
tin- i that move the foot. 

But, on the other hand, when the spinal marrow acts by 

udently of the brain, producing what is called 

reflex action, the impressions thai are transmitted, some of 

them begin, and some end, in the gray substance of the 



202 PHYSIOLOGY AKD HYGIEKE. 

spinal marrow. The impression on an excitor nerve ends 
there, and the impression on a motor nerve begins there, the 
latter resulting from the former, except when motion is 
produced by disease in the spinal marrow itself. Thus, in 
breathing, an impression goes from the lungs through exci- 
tor nerves to the gray substance, and that is the end of it; 
but another impression begins there as a result of it, and is 
transmitted to the involuntary muscles moving the chest. 

287. The Brain Rests — the Spinal Marrow 
does not. — One marked distinction between the brain 
and spinal marrow is, that the brain has its intervals of rest; 
but the functions of the spinal marrow never cease for a 
moment as long as life continues. In sleep the brain is 
more or less at rest, and it is in a state of entire torpor when 
the sleep is profound. But daring sleep the heart beats, 
the respiratory muscles w T ork the chest, and the muscular 
coat of the stomach churns the food if there be any there. 

For these motions, with many others, are dependent upon 
the spinal marrow, and not upon the brain ; and so, while 
the brain sleeps, the spinal marrow keeps up the operations 
of the system that are essential to the continuance of life. 

But beside the motions that have been mentioned, as 
being kept up by the spinal marrow, when the brain is tor- 
pid from any cause, there are other motions which can be 
excited by stimulating nerves that are connected with the 
spine. For example, the act of swallowing can be produced 
"by pouring a liquid into the mouth, and motion can be pro- 
duced in the muscles of a limb by irritating the limb at 
different points. So, too, if a man be paralyzed in his lower 
limbs by a blow upon the spinal column, these parts, which 
he cannot move by his will, can be excited to motion by 
irritation with electricity or other agents. 

It may be remarked that the voluntary muscles often act 
involuntarily. In animals from which the head has been re- 
moved, the voluntary muscles can be excited to involuntary 
action, resembling voluntary movements, although of course 
with the removal of the head were destroyed all sensation 
and all exercise of the will. A pigeon, whose cerebrum had 



THE NERVOUS SYSTEM. 203 

been removed, would fly when thrown into the air, would 
run when it was pushed, and would drink when its beak 
waa put into the water. There was no sensibility and no 
will in this case, for these cannot be without the cerebrum. 
The movements were involuntary, though performed by 
voluntary muscles. Xow as these facts prove that volun- 
tary muscles are, through their connection with the spinal 
marrow, capable of acting as involuntary muscles also, the 
question arises whether they do not much of the time act 
in part as involuntary muscles, and sometimes wholly so. 

268* Walking. — When we are walking we use volun- 
tary muscles. But manifestly a distinct act of the will is 
not put forth for every motion performed in walking. The 
mind may be at the same time fixed upon something else ; 
and there seems ordinarily to be only an occasional action 
of the will, as when we change our course, or when some 
obstacle is in the way, requiring a variation from the regu- 
lar consecutive series of movements. There is a distinct 
action of the will when the movements begin ; but after this 
the motions seem for the most part almost automatic, and 
are probably produced by the reflex action of the spinal 
marrow, the will interfering only when occasion requires. 

269. Brain not Directly JEssottial to Life. 
— Many experiments have been tried upon animals with ref- 
erence to the functions of the brain and of the spinal mar- 
row. It was formerly supposed that the brain was the only 
center of nervous power, and that it was immediately essen- 
tial to the preservation of life. But these experiments have 
shown that this is far from being the truth. The brain, it 
has teen found, has nothing to do directly with the main- 
t mance of life. Animals live for some time after the brain 
is d< A pigeon was kept alive for some months 

after its cerebrum was remored. 

[tfl condition was very much like that of a man the 

functions of wh< brum are suspended by the pressure 

of a fractured portion of 1 1 1 * - skull. Although, lik«- him, 

animal had lost all sensation and voluntary motion, yet, 

like him, it continued to breathe, and its heart continued 



204 PHYSIOLOGY AKD HYGIENE. 

to beat. Of course so extensive an injury of so important 
an organ will at length cause death ; but life continues long 
enough in such cases to show that this organ is not imme- 
diately essential to its continuance. 

270. Upper Part of the Spinal Cord directly 
essential to Life. — The functions most essential to life, 
the respiration and circulation, are, as you have seen, kept 
up by the spinal marrow. The very upper part of this organ 
is especially devoted to this purpose. You may take out 
the brain of an animal, and destroy all its spinal marrow, 
except this upper portion of it, and the animal w T ill still 
breathe, and its heart will beat. But if you destroy just this 
small portion of the spinal marrow, though you leave the 
rest of it and the brain untouched, the animal will die at 
once from the cessation of the respiration and the circulation. 

271. Effects Produced by Cutting the Spinal 
Cord. — If after cutting off the head of a frog, you divide 
the spinal marrow in the back, you can still produce involun- 
tary motions in both the upper and lower extremities. But 
the same irritation will not produce them at the same time 
in both together, for the division of the spinal marrow in the 
back separates it into two independent parts. When, there- 
fore, you irritate the upper extremities, the motion is con- 
fined to them, and the lower extremities are quiescent. And 
if you irritate the lower extremities, the motion produced 
there does not extend to the upper. The division can be 
repeated with similar results. 

If the spinal marrow be divided above and below the 
origin of a pair of nerves so as to separate this point wholly 
from the rest of the nervous system, reflex action can be 
excited in the nerves connected with this point. That is, an 
irritation of the parts supplied by the excitor nerve of this 
little segment of the spinal marrow will produce an impres- 
sion in that segment, which will be reflected by the motor 
nerve to the muscles. 

The gray substance of the spinal marrow may, therefore, 
be regarded as a chain of little brains, in some measure sep- 
arate from each other. But while there are thus many centers 






THE VOICE. 205 

of reflex action, there is only one center of sensation and 
voluntary motion, and that center, the brain, is connected 
with the mind. 

272. Tiro Systems of Nerves, Cerebro- Spinal 
and Sympathetic. — The system of nerves which we 
have been examining is termed the cerebrospinal, from its 
two great central organs, the brain and spinal marrow. 
But there is another nervous system, the functions of which 
are involved in much mystery. It is called the system of 
tlu' great sympathetic, or the sympathetic system. Some- 
times it is called the nervous system of organic life, because 
it is intimately and extensively connected with the nutri- 
tive processes: while the system that we have been consider- 
ing is called the nervous system of animal life, because it 
regulates the functions peculiar to animals: sensation, and 
spontaneous motion. 

While the sympathetic system is thus connected with the 
nutritive processes, it is also supposed to be the means of 
effecting the sympathetic connection between different parts 
of the body, and to serve as the medium through which the 
rions and emotions of the mind produce their effects upon 
the functions of the different organs. In this system there 
are many ganglions or little brains, which communicate with 
each other by nerve-. 

The structure and functions of the nervous system have 
thus been described to such an extent as will prepare you 
for the consideration of those subordinate organs, by which 
the purposes of this system are accomplished. 



CHAPTER XIII. 

THE VOICE, 

973. The Vocal Apparatus.— The apparatus of 

- truly a musical instrument. We can Bee there- 

- construction and arrangement) the applica- 



206 



PHYSIOLOGY AND HYGIENE. 



tion of those principles which usually regulate the produc- 
tion of musical sounds, and which man observes in making 
the various instruments which his ingenuity has invented to 
delight the ear. 

As the apparatus of the voice is really a wind instrument, 
we will first develop the principles on which 
Fig. 121. wind instruments produce the various 
musical notes, and then show you the re- 
semblance between these instruments and 
the set of organs which are engaged in 
producing the notes of the voice. 

Wind instruments are of two kinds — those 
that have an inflexible mouthpiece, and those 
in which the sounds are produced by a vi- 
brating reed. The horn, trombone, trumpet, 
flute, fife, flageolet, flute-stop and other 
stops of the organ, &c., are instruments of 
the first kind. 

274:. Causes affecting the Varia- 
tion of PitcJi. — The variation of notes 
produced in these instruments may be thus 
explained. The column of air contained in 
the tube is the vibrating body from which 
proceeds the sound. Any thing, then, that 
affects the size or form of the column of air 
affects the note. The length, the breadth, 
and the mode of producing tlie vibrations 
are the cause of the variation of the note. 
The holes in the side of a flute are for 
the purpose of altering the length of the 
confined column of air. In the trombone this 
is done by sliding one part of the instrument 
upon the other. The general rule is, the 
longer is the column of air the more grave 
is the note. Thus in the flute, the lowest note that can 
be produced by the instrument is made by covering all the 
holes, so that you have a column of confined air the whole 
length of the tube. The highest note, on the other hand, 



THE VOICE. 207 

which the instrument is capable of producing, is made by 
arranging the fingers as to allow the air to escape at the 
first hole. 

275. She and Width of Vibrating Column of 
Air affecting the Note* — Fig. 121 is a representation 
of one of the pipes of the flute-stop of the organ, which 
wooden box, made very much after the manner of a boy's 
whistle. At a is the passage for the introduction of the air ; 
I is the inclosed column of air, the vibration of which pro- 
duces the sound; c is the place of escape for the air; and d 
is a movable plug, by means of which the vibrating column 
of air can be made longer or shorter, according to the note 
desired. In tuning the organ, if the pipe gives too low a 
note the plug is moved downward, thus shortening the 
column of inclosed air, but if too high a note, the plug is 
raised up. 

The same rule applies to the width of the vibrating column 
of air. The wider the column the graver the note, and vice 
versa. Observe, also, that in a long, slender column of air, as 
in the trombone, by giving the current of air from the mouth 
a great velocity a high note may be produced ; but where, as 
in the ophicleide, the column is both wide and long, it is 
difficult to do this, because it is difficult to produce a quick 
vibration in so large a body of air, with all the suddenness 
and force with which we can move it. 

In those instruments which have no expedient for alter- 
ing the length of the column of air, such as the common 
horn, the various notes are produced by narrowing or widen- 
ing the orifice by the agency of the lips, as the cade requires, 
at the same tim<* giving, by the varied velocity with which 
air is forced into the instrument, a quicker or slower 
vibration to the air. Grave sounds are produced by a wide, 
and acute by a narrow opening. 

27(i* Heed Instruments. — In reed instruments the 
variations in not- are produced in a different manner. The 

•. hautboy, bassoon, the reed step- in the organ, 
are instruments of this sort it is the vibration ol the thin 
plate called the reed that causes the sound. Tin- longer this 



208 PHYSIOLOGY AND HYGIENE. 

plate is, the slower are the vibrations, and therefore the 
graver is the note. The principle can be well illustrated 
in the reed stops of the organ. The reeds in the different 
pipes are made of different lengths, according to the notes 
which they are to produce. In a reed instrument played by 
the mouth, the clarionet for example, the rapidity of the 
vibrations is regulated by the pressure of the lips. In pro- 
ducing a high note the lips press firmly on the reed and 
leave but a small portion of it to vibrate ; while in produ- 
cing a low note the lips press less firmly on the reed, and 
leave a large portion of it to vibrate. 

277. Stringed Instruments* — This same principle 
also applies to stringed instruments. Thus in the piano, 
the grave notes come from long and large strings, while the 
higher notes come from slender and short ones. In the 
violin the strings are all of the same length, the larger strings 
giving the graver notes, and the smaller the higher ones. 
The notes are varied also in the case of each string by vary- 
ing the tension. They are varied too while playing on the 
instrument by varying the length of the vibrating strings 
by the pressure of the fingers. 

278. Tube connected with the Reed. — The reed 
is frequently connected with a tube. This contains a column 
of air through which the sound caused by the vibration of 
the reed must pass. Unless, then, the vibration of this 
column of air corresponds with the vibration of the reed, it 
will alter the note. It always does alter the note to some 
extent. It never raises it, but always makes it more grave. 
That is, the vibration, in passing from the reed to the 
column of air, becomes less rapid and coarser, as is always 
the case when vibration passes from any substance to 
another. 

But the tube is so constructed that there may be as little 
change in this respect as possible. Holes are therefore 
properly placed in the side of the tube, so that with the 
fingers the column of confined air may, in the case of every 
note, be placed in correspondence with the vibration of the 
reed. 






THE VOICE. 209 

Suppose the tube to be long* and without holes; in this 
low notes could be easily produced, but attempt a 
high note and you would fail. The reason is obvious. The 
low note is caused by a low and coarse vibration of the reed, 
for the transmission of which a long column of air is fitted. 
But if a high note be attempted, the slow vibration of the 
long column of air disagrees with the quick vibration of the 
reed, and very much flattens the sound as it passes through 
the tube after coming from the reed. 

As already suggested, the object of the tube is to secure 
the combined effect of a reed and a wind instrument. 
The tube makes the reed speak, as it is expressed; that 
is, it gives intensity and an agreeable character to the 
sound. If you disconnect the reed of the hautboy or bas- 
i, for example, from its tube, and blow upon it, you 
can produce all the variety of notes, but the sound is dis- 
able; but by connecting the tube with the reed you 
produce a compound sound, as we may call it, which has a 
et and rich melody. 
We will now examine the apparatus of the voice, and see 
how for the principles which have been developed in relation 
'■omraon musical instruments are applicable to this 
instrument. 

279. Description of the Organ of the Voice. — 
at the root of the tongue, as described in the Chapter 

on the Bones, is a small bone, shaped so much like the Greek 
r v that it is called the liyoid or U-like bone. The 
curved portion of this bone is towards the root of the tongue, 
and its two ends point backward toward the pharynx. With 
connected a long cartilaginous tube extending to 
the lungs, called the trachea, or windpipe. It is through this 
tube, a.- you have already learned, that the air goes back and 
forth from the lungs in respiration and speech. It is corn- 
el of a great number of rings of cartilage connected 
ther by membranous par 

280. Lamyx.— Bui it is the upper-pari of the wind- 
pipe, that part which is immediately below the [J-like bone, 
which claims our attention as the seal of the formation of 



210 



PHYSIOLOGY AND HYGIENE. 



Fig. 122. 



the voice. This part is called the larynx. It is formed of 
five cartilages, the arrangement of which will now be shown. 
The largest of these cartilages, the one which forms most 
of the body of this music-box, as we may call it, is the 
thyroid. It is the pomum Adami, or Adam's apple, which 
is so easily felt in the top of the neck. This cartilage forms 
the front and sides of the larnyx, but it is open behind. 
The cricoid cartilage is shaped very much like a seal ring, 
and this resemblance gives it its name. The narrow part 
of it is situated directly under the thyroid cartilage, in its 

front and at its sides, but the broad, 
seal-like part of it is behind, project- 
ing upward and filling a part of 
the open space left by the deficiency 
of the thyroid in the rear. A side 
view of these parts is given in Fig. 
122, in which 1 is the U-like bone; 
4 is the thyroid cartilage ; and 6 the 
cricoid. At 8 is the back part of the 
cricoid, filling up a part of the space 
in the open rear of the thyroid ; 3 
is a horn-shaped projection of the 
thyroid, and five is a smaller one 
below, projecting over the out- 
side of the cricoid ; 2 is a strong 
membrane or ligament connecting 
the hyoid or U-like bone with the 
top of the thyroid ; 9 is the epiglot- 
tis, drawn up by a hook ; and at 7 
are the rings of the trachea. The epiglottis is composed in 
part of cartilage. It is the lid of the larynx, shutting down 
w r hen we swallow, so that the food or drink may pass over 
it, and being raised up when we breathe or speak. 

There are two small cartilages which are not seen in this 
figure, called arytenoid cartilages, from two Greek words, 
meaning ladle and shape, because they bear some resem- 
blance in form to ladles. They stand in the open space 
in the rear part of the thyroid, on the top of the cricoid 




Side view of 
THE LARYNX. 



THE VOICE. 



211 




cartilage. They are the pillars to which the vocal chords 
or ligaments are attached behind. These two cartilages are 
movable, having a regular joint with the upper edge of 
the cricoid. There are small muscles which pull them in 
different directions, and thus change the degree of tension 
and the position of the vocal ligaments, and of course vary the 
pitch of the sound produced by the vibration of the ligaments. 

281. Vocal Ligaments.— Fig. 123, is a diagram 
showing the arrangement of these ligaments. It represents 
a view of them as you look down 
into the larnyw in which a is the 
front of the thyroid cartilage, and 
bb are the two arytenoid cartilages. 
To these you see are attached two 
sheets of membrane, which are also 
fastened all around to the inside of 
the thyroid. If these movable posts, 
as Ave may call them, to which the 
ligaments are thus attached, be 
drawn backward, it is obvious that 
it will make the ligaments more 

tense. If they are separated from each other, the opening 
between the ligaments will be widened. If they are brought 
nearer together, this opening will be narrowed, and the forward 
part of the free edge of each liga- FlG 12 ± 

ment will be prevented from vibra- 
ting, because it will here be brought 
in contact with the other ligament. 

Now there are small muscles 
which are attached to the arytenoid 
cartilages for the purpose of mov- 
ing them as was pointed out. The 
figure here presented is a mere dia- 
ow tin- arrangement of 
the ligaments for the production of 
the voice, in 

124 is represented the actual appearance of the liga- 
ita and the arytenoid cartilages, as you look down upon 



Diagram showing the action of the 
VOCAL LIGAMENTS. 




Tin: VOCAL LI 



212 



PHYSIOLOGY AtfD HYGIENE. 



Fig. 125. 



them. The ligaments, you observe, are thicker at their free 
edges than any where else. 

The true vocal ligaments have been described. But there 
is another pair of ligaments directly above them, the space 
between which is the real opening into the larnyx, upon 
which the epiglottis shuts down when we swallow. In Fig. 
125 is a diagram representing the plan of these two pairs of 

ligaments, as shown by a perpen- 
dicular section from side to side. 
B B represents the vocal ligaments, 
the upper ligaments, and V V 
the two recesses between them. 

282. The Lower the True 
Voeal Chords.— We know that 
it is the lower ligaments that are 
the true vocal chords, because the 
parts above these, even the upper 
ligaments, may be all cut away, 
and yet a vocal sound may be pro- 
duced ; while if an opening be 
made into the larynx below the 
lower ligaments the voice will be 
destroyed. 

Magendie, a French physiologist, speaks of a man who, 
on account of an opening in the larnyx, was never able to 
speak without pressing his cravat tightly against this open- 
ing, in order to prevent the air from escaping through it. 
Many experiments have been tried with the larnyx after 
death to verify the results above stated. The lower liga- 
ments, then, are the vocal chords, by the vibration of which 
all the different notes of the voice are produced. And the 
other parts of the vocal apparatus serve only to modify the 
sound caused by the ligaments. The lungs act merely as 
the "wind-chest," to hold the air which, being forced out, 
strikes on the ligaments, and makes them vibrate. 

283. Principles of Musical Instruments 
applied to the Vocal Apparatus. — Let us now 
apply to this apparatus the principles already developed, as 




THE VOICE. 213 

regulating the variation of note in common musical instru- 
ments. The size of the aperture, through which the sound 
is thrown out, influences the note — of this tact we have a 
familiar example in whistling. And as you have seen that the 
size o( the opening between the vocal ligaments is varied 
by the muscles moving the arytenoid cartilages, this varia- 
tion must have an influence upon the note of the voice. 

But this is not the only cause of the variation of the 
note. As shown in relation to the reed, and to the strings 
of stringed instruments, so also here, the larger and less tense 
are the vibrating bodies, the vocal chords, the graver is the 
note. You have seen how these chords or ligaments are 
varied in tension by the action of the muscles that move 
the arytenoid cartilages. You have also seen that, as these 
cartilages are brought near together by the muscles, the 
length of the free vibrating edges of the ligaments is short- 
ened, because the edges are brought together in their an- 
terior part (Fig. 123). 

Magendie verified this by observation. He opened the 
throat of a noisy dog in such a way that he could look 
directly upon the vocal ligaments. When the sounds were 
grave, he observed that the ligaments vibrated in their 
whole length, and that the air passed out through the whole 
length of the chink between them. But when the sounds 
on a high note, the ligaments did not vibrate in their 
anterior part, but only in the posterior, and the air passed 
out only at the open part. 

2S4. Resemblance between the Instruments 
of the Voice and Common Musical Instru- 
ments.— The sound as it comes from the larynx passes 
through a tube, just as the sound coming from a reed does 
in a reed instrument In other words, there is a body of 
inclosed air extending from the larynx to the outlets of the 
month and nose, which vibrates in transmitting the sound 
from the larynx. This body of air is not SO simple in its 
form a- thai is which is inclosed in the tube of common 
I instruments. It has three outlets, the mouth and the 
two nostrils. The sound of the voice seldom comes out 



214 PHYSIOLOGY AND HYGIENE. 

from the orifices of the nostrils, but almost always from the 
mouth. In humming it comes altogether from the nostrils. 
In ordinary speaking and singing the cavities of the nose 
act as reverberating cavities, the sound which reverberates 
there issuing from the mouth. 

285. Tube of the Voeal Apparatus like that 
of a Heed Instrument. — You have seen that the 
tube connected with the reed in the reed instrument is so 
constructed, that the length of the confined column of air 
can be changed, in producing the different notes ; the vibra- 
tion of the air thus being brought into correspondence with 
that of the reed. 

If you place your finger on the front of the larynx, and 
then sound various notes, you will feel the larynx rise when 
you sound a high note, and fall when you sound a grave 
one. The object of this movement is to alter the distance 
from the larynx to the outlet of the mouth — in other words, 
to alter the length of the column of air in the tube — so that 
it may correspond in its vibration with the vibration of the 
vocal chords. But the size of this column of air is altered 
in another way. It is altered in its width, which is quite as 
effectual in changing the vibration as an alteration of 
length. The tube of the vocal instrument you readily 
see can be altered in its width by the muscles of the throat 
and mouth. 

The object of the tube of the reed instrument is to make 
the reed speak, as it is termed ; that is, to give intensity 
and an agreeable character to the sound. If the voice 
should come directly from the larynx without passing 
through the tube attached to it, it would be as disagreeable 
as the sound of a reed when separated from its tube. 

The voice gets most of its melody after it is made in the 
larynx, as it passes out through the column of air in the 
throat and mouth. And it is the variations of this tube 
produced by the muscles that surround it that give to the 
voice its variety of tone as well as its melody, thus consti- 
tuting one of the great excellencies of the vocal instrument 
in comparison with all common musical instruments. 



THE VOICE. 215 

286. Delicacy of the Action of the Focal 

JIuscIes. — To have some conception of the variety of the 
motions oi^ the muscles concerned in the modulation of the 
voice, listen to some singer whose voice can command with 
and freedom a great extent of the scale. For every 
note that you hear there is a distinct and particular adjust- 
ment of the vocal ligaments, and of course a particular de- 
• of contraction of the little muscles that move them. 
It is calculated that the ligaments vary in length only 
about the \ of an inch in producing all the notes of the 
voice. Now the natural compass of the voice (that is, its 
range from its lowest to its highest note) in most singers is 
it two octaves or 24 semitones. Within each semitone 
a singer of ordinary capability can produce 5 or G distinct 
notes; so that for the whole number of notes that he can 
sound distinctly 120 is a moderate estimate. He therefore 
produces 120 different states of tension in the vocal liga- 
ments. And as the variation in their length for passing 
from the lowest of these 120 notes to the highest is only 
the -i-th of an inch, the variation required to pass from one 
note to another will be only the -g-J-Q-th of an inch. A very 
■rt singer can produce a much more delicate action than 
this, and distinctly appreciate the result by his ear. 

'ISi. Importance of Keeping the Chest Full 

of Air. — The skillful singer or speaker exhibits much 

skill in managing the muscles of the "wind-chest." He 

pa it all the time well supplied with air, so that but a 

comparatively slight action of the expiratory muscles will 

suflice to throw the air against the vocal ligaments witli the 

requisite force. But an unskillful singer or speaker much 

<>t* til.- time has his chesl poorly supplied with air, and so 

as it is expressed, from the lop of the chest. 

him, therefore, so much labor to throw out the air 

with sufficient fore-, that he is soon tired out. 

Th jsity for keeping the chesl full of air. in order to 

work tli.; vocal apparatus easily, may be illustrated by refer- 

igpipe. [f the bag containing the air be well 

filled, a slight pressure of the arm upon it will force the air 



216 PHYSIOLOGY AND HYGIENE. 

through the pipe with' sufficient rapidity to produce the 
sound. But if the bag be flaccid from the little quantity 
of air in it, a very strong pressure of the arm will be re- 
quired to produce the same effect. 

288. Tiring out the Vocal Muscles.— But it is 
not the muscles of the chest only that are tired out in the 
unskillful singer or speaker, but also the muscles of the 
larynx and the throat. And a frequent tiring of these 
muscles weakens the parts, and often at length produces 
disease. Much of the throat-disease of public speakers 
comes from this cause, and is a nervous disease, the affection 
of the lining membrane of the throat being often a mere 
accompaniment. 

This result is more apt to occur when the nervous force 
of the system generally is impaired. It is also more apt to 
occur in those who speak in a uniform and somewhat 
monotonous manner, than in those who speak with much 
variety. A continuation of precisely the same muscular 
effort for any length of time is apt to produce painful 
exhaustion, while a much greater amount of varied muscu- 
lar effort may be put forth without weariness, or even with 
pleasure. 

289. Parts Engaged in the Articulation 
of the Voice. — We will now observe the agency of the 
different parts of this compound vocal tube in the articu- 
lation of the voice. Each letter, whether it be a vowel 
or a consonant, requires a particular position of the differ- 
ent parts of the vocal tube. In some letters the tongue 
is the chief agent in articulation, in others the lips, in 
others the teeth, in others the palate, and there are some in 
the formation of which the cavities of the nose have an 
important agency. 

290. The Tongue less Essential than Com- 
monly Supposed. — The tongue has been considered so 
essential to speech, that tongue and language are often used 
synonymously. But though it does perform an important 
part in articulation, it is not absolutely essential. A boy, 
who lost his tongue by disease at the age of eight years, was 






THE VOICE. '-217 

exhibited publicly because he could talk without a tongue. 
A girl, who lost from disease the whole of her tongue, to- 
gether with the uvula (the little round body which hangs 
down from the middle of the arch of the palate), could talk 
and swallow as well as any one. So perfect was her articu- 
lation, that she could pronounce with exactness those letters 
which commonly require the agency of the tip of the tongue. 
She could sing finely, articulating with the same clearness 
as when she talked. 

29 I* Dentals.— Some of the letters are formed princi- 
pally by the teeth, as c, t, s 9 z. They are therefore called 
Dentals. It is the too frequent and bungling employment 
of some of these which constitutes lisping. Those who have 
a tongue too large for the mouth are apt to lisp. In advanced 
when the teeth are lost, we find this defect of lisping. 
The reason is obvious. When the teeth are gone, the sockets 
gradually become obliterated, and that part of the jaw T -bone 
where the teeth were, of course diminishes in size, making 
the mouth too small for the tongue. 

21)2. Labials. — The letters, in the articulation of 
which the lips takes the lead, are b, p, m, f, v, w, &c, 
and are called labials. Children, when they first begin to 
talk, use labials freely, because they can see in others the mo- 
tions necessary for their pronunciation, and are led to imitate 
them. H mce the endearing terms used by the child to the 
parent are. in all languages, or nearly all, composed of labials 
and vowels. And, too, it is from the delight which the child 
takes in r peating over and over these terms, that we have 
the word papa and mama, instead of pa and ma. The same 
thing can be observed in other languages as well as the 
English. 

293. Reverberation in some Letters in the 
Nasal Cavities. — The nasal cavities, it is obvious, must 
have a Ln^at influence in articulation. The letters?/! and n 
are partly nasal. In pronouncing in at the end of a syllable, 
/.«.]- om,we close the lips, and the sound issuing 
from the larynx reverberates in the cavities of the nose. You 
can v. rb< -ration bv pressing gently upon the 



218 PHYSIOLOGY AND HYGIENE. 

nostrils with the fingers while pronouncing this letter. 
The same can be said of n, except that in pronouncing it 
we press the tip of the tongue against the roof of the mouth 
just behind the front teeth, preventing the passage of the 
air out through the mouth in this way, instead of doing it 
by closing the lips, as in articulating m. 

294. Speaking through the Nose. — In what is 
commonly called speaking through the nose the reverbera- 
tion mentioned above is disagreeably strong. The popular 
idea of it is incorrect, for this fault occurs in those who have 
some obstruction to the free passage of the air through the 
nose. This obstruction acts like the pressing of the nostrils 
with the fingers, confining more or less the body of air con- 
tained in the nasal passages. It is the vibration of this air 
thus partially confined in tortuous passages that produces the 
nasal twang. Any thing, therefore, which prevents the free 
outlet of the air from the nose will occasion it. Pressing the 
fingers on the nostrils while speaking will produce it. 

295. Whispering. — When no sound is produced by 
the ligaments of the larynx, as is the case in whispering, the 
noise produced by the passage of the air through the cavities 
of the vocal apparatus can be so articulated, as to be heard 
distinctly at a considerable distance. Persons, therefore, 
who have entirely lost the voice can converse. In whisper- 
ing the vocal ligaments are relaxed as they are when Ave 
simply breathe. But the sound of whispering has its high 
and low notes like the vocal sound. The variation of note 
is caused by variation of the size of the column of air con- 
tained in the vocal tube. 

296. Contrivances to Imitate Articulation. — 
Various attempts have been made to imitate the articulation 
of sounds by mechanism, but with very limited success. In 
1779 a prize was offered by the Academy of Science at 
St. Petersburg, for the best dissertation on the theory of 
vowel sounds, and it was awarded to G. E. Kratzanstein, an 
account of whose experiments was published in the Trans- 
actions of the Academy. He found that the sound of the 
four vowels, A, E, and U, might be produced by blowing 



THE EAR. 



219 



through a reed into tubes, the forms of which are repre- 
sented in Figures 126, 127, 128, 129 and 130, and that the 

Fig. 126. Fig. 127. Fig. 128. Fig. 129. Fig. 130. 





sound of I, as pronounced by the French and other European 
nations, could be produced by blowing into the tube, Fig. 
130, at a, without using the reed. 



CHAPTER XIV. 

THE EAR. 



In the last chapter the production Qf sound by the vocal 
apparatus was mentioned. In this chapter it is proposed to 
show how the impression of sound is transmitted to the 
brain, in order to produce the sensation of hearing. 

297. Difference between ft Sound and a Noise. 
— Sound may be produced by the vibration of any substance ; 
though some bodies are better fitted to produce it than others, 
and are therefore called sonorous. When the vibrations 
which cause sound are equal, a musical sound results; but 
if they are unequal, we have a discordant sound, or what Ave 
ordinarily call a noise. Sound is transmitted from the point 
where it originates, in all directions. And its vibrations 
gradually lessen, just as the ripples lessen which are pro- 
duced by dropping a stone into the water. 

298. Reflection of Sound.— The vibrations of 



220 PHYSIOLOGY AND HYGIENE. 

sound are reflected by objects against which they strike. 
For this reason the voice can be heard at a much greater 
distance if it be transmitted along a wall than when it is 
uttered in an open space. This may be illustrated on Fig. 
131. Let A B represent a wall, and C the position of the 

Fig. 131. 



ear. If the bell at D be rung, besides the vibrations which 
come to the ear at C in the direct line C D, a vibration strik- 
ing the wall at F will come to the ear in the line F C, and 
the same can be said of other points along the wall. An 
accumulation of vibrations, therefore, comes to the ear at C, 
which therefore receives a louder sound from the bell than 
it would if the bell were rung in a perfectly open space. 
For the same reason a speaker can be heard much more 
easily within walls than in the open air. The sound is 
reflected, and, therefore, in some measure concentrated by 
the walls. 

299. Speaking Tube. — In speaking tubes this reflec- 
tion and concentration are carried to a still greater extent. 
Sound can in this way be heard at a great distance from its 
source. M. Biot found that when he spoke in a whisper at 
one end of a tube, over three thousand feet in length, he 
was distinctly heard at the other end; so entirely do the 
walls of the tube prevent the diffusion of the vibration in 
the air around. Speaking tubes are therefore used to a 
great extent in large manufactories, where directions need 
to be given continually to workmen in different parts of the 
establishment. The flexible tube, now so commonly made 
use of by deaf persons, furnishes another illustration. The 



THE EAR. 221 

vibrations of the voice received by the trumpet-shaped end 
are transmitted through the tube to the ear. 

:>00. Difference in the Transmission of 
Sound through Solids, Liquids and Gases. — 

Sound may be transmitted through any substance, whether 
it be solid, liquid, or gaseous. It cannot he transmitted 
through a vacuum, for there is nothing there to vibrate. 
Sound differs in this respect from light, which passes as 
readily through a vacuum as it does through any transparent 
substance. 

A pistol fired on the summit of a mountain, gives not 
nearly so loud a report as when it is fired in the valley below. 
The more solid the medium is for the transmission of 
sound, the more readily is it transmitted. The scratching 
of a pin at the end of a long log may be heard by the ear 
applied to the other end, although it can not be heard through 
the air, at even the distance of a few feet. A deaf gentleman, 
resting the bowl of his pipe on his daughter's piano-forte as 
he smoked, found that he could hear the music with great 
distinctness ; and many deaf persons can hear conversation, 
by holding a stick between their teeth, while the other end 
rests against the teeth of the person speaking. 

Water is a much better conductor of sonorous vibration 
than air, though it is not so good an one as a solid substance. 
The force of the vibration is lessened more gradually in 
water than in air, and its rate of progress in water is, accord- 
ing to Chladni, 4,900 feet in a second, or between four and 
five times as great as in air. 

30 1. Sonorous Vibration does not j> ass 

readily from one Medium to Another. — Thus, 

although the scratch on the log is heard so easily by the ear 

at the other end, if the far be removed a little from the log, 

it does not hear the sound, because the vibration is so much 

: in passing from the .solid wood to the air. It is 

r that the more unlike two substances are, when sound 

from one to the other, the more will the force of the 

vibration b d ; for the more unlike they are, the less 

easily will the one take the vibration from the other. 



222 PHYSIOLOGY AXD HYGIENE. 

For this reason, a sonorous vibration, produced in a solic 
body, may be transmitted to water with much less loss o1 
intensity or force, than occurs when it is transmitted to air. 
And it may be remarked in this connection, that when vibra- 
tions are transmitted to a fluid, from air or from a solid, an 
intervening membrane is of essential service, for it pre- 
sents a firm surface upon which the vibrations can be received. 

302. Hearing a Compound Process.— The 
vibrations of sound, passing into the ear by a tube, strike at 
the bottom of that tube upon a membrane called a drum 
The air can go no farther, for this drum is perfectly air-tight. 
It communicates its vibrations, however, to the drum, which 
transmits them to a chain of four little bones, the last of 
which transmits them to another drum, covering an opening 
into various winding passages in solid bone. In these 
passages is contained a limpid fluid, which is put in motion 
by the vibrations of the drum last mentioned. 

So much for the mere mechanical part of the process. In 
the winding passages are spread out the minute fibres of the 
nerve of hearing. The vibrations of the liquid in these halls 
of audience make an impression upon these nerves, which 
is communicated to the brain through the trunk of the 
nerve, and this completes the whole process necessary to the 
production of the sensation of hearing. 

303. The Parts of the Apparatus of Hearing 
Described. — The parts of the apparatus of hearing may 
be seen in Fig. 132. The internal portions are made rather 
larger than natural, in order that the construction of the 
ear may be clearer. At a I c is the external ear ; at d is the 
entrance to the tube of the ear,/; g is the drum of the ear at 
the end of this tube, called the membrane of the tympanum; 
h is the cavity of the tympanum, the chain of bones which it 
contains being left out, so that the plan of the apparatus may 
be more clear to you ; Tc is the Eustachian tube, which 
makes a communication between the back of the throat 
and the cavity of the tympanum ; n is a part of the 
winding passages, shaped like a snail's' shell, and therefore 
called the cochlea; at m are three other winding passages, 






THE EAR. 



223 



called, from their form, semi-circular canals; and at I is the 
vestibule, or common hall of entrance to all these winding 
passages. 




* * b f b 

VERTICAL SECTION OF THE ORGAN OF HEARING. 



In the wall of the tympanum, on the side opposite to 
the drum of the ear, you see two holes. These open into 
the winding passages, the larger one into their vestibule or 
entrance hall. Each of these holes is covered by a mem- 
brane, and to the membrane of the larger one is attached 
the last of the chain of bones. At o is the trunk of the 
nerve of hearing, and at e e is the bone that encloses these 
parts, which is so hard that it is called the petrous, or rock- 
like bone. 

804, External Ear. — The object of the external ear 

collect the waves of sound, and direct them into the 

tube of the ear. There have been many speculations in 

regard to the use of the prominences and ridges of the 



224 PHYSIOLOGY AND HYGIENE. 

external ear, but they are fanciful and groundless ; and its 
surface is thus diversified, probably for the sake of comeli- 
ness. If the object were to give it the best shape and 
construction for collecting the vibrations of sound, it would 
have had a different shape altogether, and would have been 
provided with muscles which could turn it in different 
directions, as is the case with many animals. The shape of 
the external ear is much better in many animals than it is 
in man, if we consider its object to be merely the collection of 
the waves of sound. The endowment is in this case, as well 
as in every other, according to the necessities of the case. 

305. Tube. — The tube of the ear is about an inch long 
in the adult. It is formed of cartilage like the external ear, 
and ends at the drum. At its entrance are hairs which 
afford some protection against intruders. But the chief 
protection is the bitter wax, which is secreted by little 
glands, situated in the skin of the tube. The odor from 
this secretion so effectually keeps out the insects from this 
open entrance, that it is quite a rare occurrence to have an 
insect get into the ear. And when one does get in, the 
wax envelopes him, and commonly soon destroys him. 

306. Drum and Hones. — The drum of the ear, 
which makes the closed end of the tube above described, as 
seen at g, Fig. 132, is very thin and transparent. On the 
other side of it is the cavity of the tympanum h. In this 

cavity are the four bones. These 
Fig. 133. are represented in Fig. 133, en- 

larged so that you can see their 
shape distinctly. They are 
named from their shapes. 

They are the malleus or ham- 
mer m; the incus or anvil i; the 
os orbiculare, or round bone o, 
the smallest bone in the body ; 
and the stapes or stirrup-bone. 
The long handle of the hammer h is fastened to the middle 
of the drum of the ear. The little round bone is fixed 
between the slender end of the anvil, and the top of the 





THE EAR. 2^5 

stirrup-bone. In Fig. 134 you have a representation of 
these bones, together with the drum of the ear. While the 
end of the handle of the hammer is fastened to the middle 
of the drum, the base of the stirrup is 
fastened to another drum, covering the Fig. 134. 

hole or window, opening into the vesti- 
bule of the winding passages. 

There are three very delicate muscles 
which move these bones. One of them 
relaxes the dram of the ear, and another 
makes it more tense : and thus the drum 

L - j , , • , , p , • DRUM OF THE EAR 

is put into the right states of tension, to with the bones 

accommodate it to the various kinds of 
vibration that come to it. This is a matter of some import- 
ance, for it is plain that while a relaxed drum can vibrate 
properly to grave sounds that enter the ear, it must be tense, 
in order to respond properly to the vibrations of the air in 
the higher notes. 

307. Eustachian Tube. — The cavity of the tympa- 
num (A, Fig. 132) containing the little bones, which is 
beyond the drum, communicates with the mouth by the 
Eustachian tube l\ If you shut your mouth, and close the 
nostrils with the fingers, and then perform the action of 
blowing, you will feel the air enter the Eustachian tubes, and 
fill the cavity of the tympanum. The chief object of this 
communication is to have air on the inside as well as the 
outside of the drum, so that it may vibrate freely. 

SOS. Winding Passages of the Internal Ear. 
— These are inclosed, as already stated, in the most solid 
in the body. They are called together, very appro- 
priately, the labyrinth, sometimes the internal ear. This is 
really the essential part of the apparatus. Here are the true 
halls of audience, where the nerve receives the messages 
from without, and transmits them to the brain. The drum 
of the ear and the chain of little bones may be destroyed, 
and yet, if these winding passages remain cut in 1 , with the 
ibranes over the two windows that open into them, the 
hearing will not be lost ; though it will be less perfect than 



226 



PHYSIOLOGY ASD HYGIENE. 






Fig. 135. 



it is when the whole of the apparatus is there, and in good 
order. 

309. The Winding Passages. — The labyrinth is 
represented much magnified in Fig. 135. The middle part 

of it, v, is the vestibule. From 
this go out the semi-circular 
canals, x, y, z, on the upper 
side, and on the lower the 
winding passages of the coch- 
lea, k. At o you see the open- 
ing called the fenestra oralis, 
or oval window. This is cov- 
ered by a membrane, on which 
presses the base of the stirrup- 
bone. You see another open- 
ing, r, which is called the fen- 
estra rotunda, or round win- 
dow. This is covered with a 
membrane. Both of these 
openings you see in Fig. 132 

in the wall of the tympanum, opposite to the drum of the 

ear. 

310. Principles of Transmission of Sound 
observed in the Arrangement. — It will be proper to 
say a word here in relation to the choice of a fluid, instead 
of a solid or an aeriform substance, as the medium through 
which the impression of the vibration of sound is communi- 
cated to the nerve. It is better than a solid would be, 
because no arrangement of a vibrating solid with the minute 
fibres of the branches of the nerve could be effectual, and at 
the same time so little liable to derangement, as the arrange- 
ment of nervous fibres immersed in a liquid, and the whole 
inclosed in solid walls of bone. 

It is better than air would be, for at least two reasons. 
1st. The vibrations of sound are communicated with much 
more ease and rapidity through water than through air. 
This we see to be a consideration of some importance, when 




THE EAR. 227 

we look at the complicated and winding passages that con- 
tain the fluid. 

*-2d. There is not so much loss in the force of the vibration 
in the transmission from the solid stirrup-bone through 
the membrane to the fluid, as there would be if the transmis- 
sion were to air. 

311. Steps of the Process of Hearing given 
in their Order. — Having thus described the parts of the 
organ of hearing, we will trace the steps of the process of 
hearing, as it must occur in the case of every sound that 
we hear. The vibrating air enters the tube of the ear, 
and, reaching the drum, produces a vibration there. This 
vibration is communicated to the chain of bones, which 
pass it on. It is transmitted from the last of this chain 
of bones, the stirrup-bone, to the membrane covering the 
fenestra oralis, and from this to the fluid contained in all 
the passages of the labyrinth. 

The vibration goes through all the semi-circular canals in 
one direction, and in another up one gallery of the cochlea, 
and down the other. In all these cavities, are spread out in 
various ways the filaments of the nerve which receive the 
impression of the vibration. This impression is transmitted 
from the extremities of the nerve, through its trunk, to the 
brain, where the mind receives it. All this together consti- 
tutes hearing ; and all of it occurs in the case of any sound 
which we hear, however closely it may follow any other 
sound. 

Most of our hearing is done precisely in the way described, 
but not all. We sometimes hear directly through the bone 
surrounding the labyrinth. If you place a watch between 
the teeth, you hear the ticking; and it gives a very different 
sound from what it does when held to the ear, because the 
sonorous vibration is transmitted directly from the teeth 
through the solid bones of the skull. 

312. Complicated Apparatus, producing 
Simple Results.— Though the apparatus of the ear is 
complicated, the mechanical result is a simple one— it is a 



228 PHYSIOLOGY AND HYGIENE. 

mere trembling of a fluid inclosed in winding cavities of 
bone. But simple as the result is, it is made, through the 
beautiful nervous connections of the ear with the brain, one 
of the chief inlets of knowledge to the mind. 

Thus intimately in the human body are the simplest 
mechanical results connected with the complicated and 
diversified operations of the mind. In the process of hear- 
ing the drum of the ear is to be considered one end of the 
apparatus, and the gray portion of the brain the other. The 
drum simply vibrates ; and instantaneously the mind receives 
a distinct impression from the vesicles of the gray matter. 
And thus is the communication established between the 
immaterial mind, and the vibrations of the material sub- 
stances with which it is surrounded. 



CHAPTER XV. 

THE EYE, 

313. Seeing, a Compound Process.— The sen- 
sation of sight is the result of a compound process, which 
may be divided into two distinct parts. The one part is 
purely mechanical, and the apparatus for it is constructed 
according to the common principles which we find illus- 
trated in optical instruments. The object of its arrange- 
ments is to form distinct images of objects in the back part 
of the eye. The other part of the process is executed by the 
nerve of vision, called the optic nerve. 

314. He fraction of Light. — The rays of light com- 
ing from any luminous point go in straight lines in all direc- 
tions, just as the vibrations of sound do, and, like them, 
become less intense the farther they are diffused. When 




THE EAR. 229 

they pass from one medium into another they are bent out 
of their straight course, or refracted, unless they pass from 
one to the other in lines perpendicular to the surface of the 
medium which they enter. 

315* Refraction us Lir/Itt passes from a 
Barer into u Denser Medium, or Vice Versa. 
— This may be illustrated by the following experiment, 
e a coin, a, in the bottom of a basin, as represented in 
Fig. 136, and then withdraw from 
it so far that the coin may be hid- Fig. 136. 

den from your eye by the edge of 
the basin, as represented in the 

figure. Keeping your eye fixed in / y e 

that position, pour some water into 
the basin up to the level, c. The coin 
will again become visible to your eye. 
The reason is. that the rays of light, 
as they come from the water into 
the rarer medium, the air, are re- 
fracted or bent downwards, that is, from the perpendicular. 
The effect of this may be seen in the figure. A ray of light, 
coming from the coin in the direction a, d, does not pass to 
dy but is bent downward, and so passes to the eye at c. The 
coin, therefore, is Been by the eye at c, but it is not seen in 
its true direction from the eye, which is in the line e, c, <7, 
for we always judge of the place of an object by the direction 
in which the rays from it strike the eye. The only point 
from which the eye can see the coin in its true position is 
at J> % in a perpendicular line directly over it. A ray that 
passes from one medium to another in a line perpendicular 
to the surface of tie- medium into which it passes is not bent 
out of it- course. 

While rays that pass from a dense medium into a rarer, as 
from water into air, are bent from the perpendicular, those, 
on the other hand, which pass from a rarer medium into a 
s from air into water, are bent towards the perpen- 
dicular. Thus if in Fig. 136 a be tie- position of the eye <>l 
a fish., and where th . ut *, there he an insect, the fish 



230 PHYSIOLOGY AND HYGIENE. 

can see it, because the ray that strikes the surface of the 
water, c, is refracted or bent towards the perpendicular line, 
b, a. He does not see the insect, however, in its true direc- 
tion, a, c, e, but it appears to him to be at d. 

316. Refraction by Convex Lenses.— When 
light passes from one medium into another of different 
density which presents a convex or concave surface, instead 
of a flat one, a very great change is produced in the direction 
of its rays. Thus suppose, as represented in Fig. 137, three 

Fig. 137. 






diverging rays coming from a point, a, through the air, 
enter a convex surface of glass, I, V. The central ray a, c, 
enters the glass in a direction perpendicular to its surface, and 
therefore does not bend from its course. But the ray a, d, 
enters very obliquely, and is bent towards the perpendicular 
at that point, e, and passes on in the direction /. So like- 
wise the ray a, g, is bent tow r ards the perpendicular h, and 
passes on in the line i. These rays diverging in the air have 
become converging in the glass, and the point at which they 
meet is called the focus. To this point all the other rays 
entering the convex glass converge also. 

317. Refraction by Concave Lenses. — But if 
the surface of the glass be concave, as represented in Fig. 
138, the diverging rays which enter it will be made to 
diverge still more. The ray, a,c, being perpendicular to the 
surface is unchanged in its course ; but the ray, a, d, is bent 



THE EYE. 



231 



towards the perpendicular, e, into the line /, and the ray, 
a, /, is bent towards the perpendicular h into the line i. 



Fig. 138. 




In the case of both the concave and the convex lens, the 
greater the curvature, the greater is the change of direction 
in the rays. The greater the curvature, therefore, the 
sooner are the rays brought to a focus in the case of the 
convex lens. 

Fig. 139. 




DIFFERENT PARTS OF THE EYE. 



318. Description of the Coats of the Eye. — The 

arrangement of the different parts of the eye is shown by 
Fig. 139, which is a mere map of a section of the eye, through 



232 PHYSIOLOGY AND HYGIENE. 

its middle part from front to rear. It is intended to repre- 
sent the arrangement of the parts distinctly, without strict 
regard to proportion. The eye has three coats, as they are 
called. At a is the thick strong white coat, called the scle- 
rotic coat, from a Greek word meaning hard. This, which 
is commonly called the white of the eye, gives to the eyeball 
its firmness. Into it the cornea, e, fits like a watch-glass 
into its case. The sclerotic and cornea then make the outer 
coat of the eye. 

Next comes the choroid coat, 6. This is a very vascular 
coat, containing the minute branches of blood-vessels which 
nourish other parts of the eye. It is of a dark color, for 
reasons which will be stated in another place. Its color is 
owing to coloring matter contained in pigment cells, which 
lie along on the inner surface of this coat, next to the inner 
coat of the eye, the retina, c. The retina is a thin mem- 
brane, being principally composed of the expansion of the 
optic nerve, d. 

319. Humors of the Eye. — The eye has three 
humors, as they are termed. The first is the aqueous or 
watery humor,/, which is in a chamber between the trans- 
parent cornea, e, and the crystalline humor, or lens, h. 
This chamber is divided into two parts by the iris, g, g, the 
pupil being the circular communicating door between them, 
The part of the chamber which is in front of the iris is much 
larger than that which is behind it. The crystalline humor, 
or lens, as it is more often called, has the consistency of half 
dissolved glue. At i is the vitreous humor, filling up a large 
part of the cavity of the eye. It is called vitreous from its 
glassy appearance. It is a clear jelly-like substance, having 
about the tenacity of white of egg. It is contained in an ex- 
ceedingly thin and delicate sac, and this is divided into cells 
which contain the liquid. 

320. Arrangement of the Front Part of the 
Eyeball. — Fig. 140 is a map of the front part of the eye, 
in which the parts are more minutely delineated than in Fig. 
139. At 2 is the sclerotic coat ; 3, the cornea ; I, the crys- 
talline lens; a, a, a, the aqueous humor; 7, 7, the iris; 4, 



THE EAR. 



233 



Fig. 140. 



the choroid coat; 8. the retina; c\ c, the vitreous humor; 
and 9, the sac containing it. Around the inside of the 
chamber containing the aqueous humor is a very thin mem- 
brane (represented as you see by 
a line), which secretes the humor. 
In this membrane, as in the case 
of every other closed sac in the 
body, there are both exhalants 
and absorbents, so that the fluid 
may be changed as necessity re- 
quires. 

There is another thin mem- 
brane of the eye which has not 
yet been described. It is repre- 
sented by a line, 1, in the figure. 
It is the conjunctiva, so called 
because it unites or conjoins the 
ball of the eye with the eyelids. 
It covers the cornea, passes back 
a little way on the white of the 
eye, and then turns forward to 
line the eyelid. It is the seat of 
the most common form of inflam- 
mation in the eye. It is very vascular, as is shown by its 
distended vessels when it is inflamed. It is exceedingly sen- 
sitive, and hence the great pain which is occasioned by any 
thing, even the smallest mote, that gets into the eye. 

321. Ciliary Processes. — At G in Fig. 140, is one 
of the ciliary processes, as they are called, from their resem- 
blance to the eyelashes. There is a circular row of them, 
numbering from sixty to eighty, so arranged as to resemble 
the disk of a radiated flower. In Fig. 141 they are repre- 
sented as they appear in looking at them from behind, the 
k parr of the eye being removed. At 1 is the divided 
edge of the three coats; -'.the pupil; 3, the iris; 4, the 
ciliary processes. At 5 i> the anterior edge of the retina, 
at the beginning of these pr presenting, us yon 

see, a scalloped appearance. The processes come from 




234 PHYSIOLOGY AND HYGIENE. 

choroid coat, and are united at their origin by a ring of 
ligamentous substance to the sclerotic coat. The exact 
operation of this beautiful mechanism is not known, but 




CILIARY PROCESSES 

it is pretty well ascertained, that muscular fibres are so con- 
nected with these processes, that when they contract they 
draw the crystalline lens forward. 

322. Object of the Apparatus to Form Images 
of Objects on the Retina. — The object of all this appa- 
ratus, here described, is the formation of images of objects in 
the back part of the eye upon the retina, so that the optic 
nerve expanded there may carry impressions from them to 
the brain. The rays of light coming from an object pass 
through first the cornea, then the aqueous humor, then the 
crystalline lens, and lastly the vitreous humor to the retina, 
where they, so to speak, daguerreotype the object. The fact 
that such an image is formed has often been proved by 
observation on the eyes of animals. 

If the eye of a rabbit be cleansed from the fat and 
muscles at its back part, and a candle be held in front of it, 
you can see the image of the candle through the sclerotic 
coat, formed upon the retina. So if you take the eye of an 
ox, and carefully pare off the back part, so as to leave it very 



THE EYE. 235 

thin, a distinct image of any tiling placed in front of the eye 
may be seen at the back part. 
323. Images on the Retina Inverted. — The 

image, however, will be inverted, as represented in Fig. 1-42. 

Fig 142. 




For the sake of clearness two rays only are represented as 
coming from each of the two ends of the object, a, c. These 
rays cross each other in the middle of the eye, those from a 
being brought to a focus at b, and those from c at d. As 
all the other rays, coming from other points in the object, are 
refracted in the same manner, a complete inverted picture 
of it is thus formed. The cornea is, as you see by Fig. 139, 
more convex than the sclerotic coat, so that it may act with 
some power as a lens in making the rays converge. 

324. Iris. — The iris is a circular curtain with a round 
opening in its center, called the pupil. The latter can be 
varied in size to a considerable degree. On the iris depends 
what is called the color of the eye, which is various, as blue, 
nearly black, gray, hazel, &c. The chief office of the iris 
La to regulate the quantity of light that enters the eye. 
When the light is obscure, the opening in the 
iris is widely dilated ; but when there is much 
light it is contracted ; and if the light be 
excessive, it is contracted almost to a point. y ](] \ 43 
These motions are effected by peculiarly ar- 
ranged muscular fibres, of which the iris is in 
parr composed. There are two Bets of fibres, 
the circular and radiated, as represented in 
Fig. 143. When the circular fibres contract, 
the pupil is contracted : and when, on the other hand, the 
radiated fibres contract, the pnpil is dilated. 

326. Crystalline Lens. — The crystalline lens is the 




236 PHYSIOLOGY AND HYGIENE. 

chief agent in the eye in concentrating the rays of light by 

refraction. In Fig. 144 you have a side view of it. Its 

anterior part, 1, is less convex, than its posterior, 

Fig. 144. 2. In Fig. 145 is a magnified view of the lens 

§ hardened in spirit and cut open, so as to show 
the different layers of which it is formed. The 
2 layers are more and more hard as you go towards 
the center. The object of this arrangement and 
Lens °^ ^ e P ecra li ar shape of the lens, is not as yet 
understood. 

326. Choroid Coat.— The choroid coat {b, Fig. 139) 

contains quite a large share of the 
Fig. 145. minute blood-vessels and nerves of 

the eye, and serves for a medium 
by which they pass to other parts 
of this organ. But it serves an- 
other important purpose by means 
of its dark pigment. It makes a 
dark chamber of the back part of 
the eye where the optic nerve is 
expanded. The object of this is to 
secure distinctness in the images 
formed upon the retina. 

32 7. Want of Pigment in the Choroid of the 
Albino. — The pigment is deficient in the iris of the 
albino ; and the bright red or pinky hue of the iris in his 
case is owing to the blood in the minute blood-vessels, with 
which this part is so well supplied. Those animals that use 
their eyes mostly in daylight have the pigment of the 
choroid of the darkest color ; while, on the other hand, 
those that need to see most clearly at night, as the owl, 
either have none of this pigment, or have it of a very light 
color. 

328. The Retina.— The retina is a soft grayish deli- 
cate membrane, formed chiefly of the expansion of the 
optic nerve. Here the images are formed, and the minute 
fibres of nerve in this membrane receive impressions from 
these images, which are transmitted to the brain by the 




THE EYE. 



237 



Fig. 146. 



trunk of the nerve. This nerve has the same relation to 
light that the nerve of hearing has to sound, the nerve of 
smell to odors, or the nerve of touch to the qualities of 
bodies that we feel. And it is curious to observe that the 
termination of the nerve of sight on the surface of the retina 
is arranged in papilla, just as the terminations of the nerves 
of touch are. In Fig. 146 is represented a portion of the 
retina of a frog magnified three hun- 
dred times. The upper rows of papilla}, 
which are without dots, are seen side- 
ways. 

329. Spherical Aberration.— 
There is a defect in the operation of 
lenses in optical instruments, which is 
k rmed spherical aberration. This can be 
explained on Fig. 147, which represents a lens, L, L', with 
some of the rays as they pass through it. Now the rays 
R' R" IV are brought to a focus at F ; while the rays R L 
and R "" L' come to a focus much nearer, at I It is found by 




Fro. 147. 




experiment, that if the central portion of the lens be covered, 

that the rays R' R IV" cannot pass, a distinct image 

will be formed on a screen put at /. And, on the other 

hand.it' the outer portion of the lens be covered, so that 

outer rays are intercepted, then the middle rays, E' \l B 
will form an image on a screen ai P. Bui if the whole lens 
be used, no distinct image is formed, anywhere. U you 



238 PHYSIOLOGY AND HYGIENE. 

place the screen at I, it will receive, with the rays that come 
to a focus there, rays that have their focus at F. 

In the eye the iris acts as the diaphragm or stop to 
the crystalline lens which is behind it, as was indicated in 
Fig. 139. Ordinarily, by means of this stop, the rays pass 
through only the central part of the lens. 

330. Chromatic Aberration, — Another difficulty 
attending the operation of a common lens is what is termed 
chromatic aberration. Every ray of white light consists of 
a mixture of rays of seven different colors. Some of these 
colors are more easily refracted than others, and therefore 
on passing through a lens will come to a focus sooner. This 
of course is apt to make some confusion in the color and 
the distinctness of objects, when seen through a single lens, 
or through several if they are alike. 

The difficulty has been remedied, and it is said that the 
hint of the remedy was taken from the arrangement of the 
eye. At any rate, the defect is avoided by having lenses 
made of different materials, just as is the case in the eye. 
Thus if two lenses be used, one of which is made of flint 
and the other of common glass, the difficulty disappears. 
In the eye it is perfectly avoided by the passage of the rays 
through so many different materials, before they reach the 
retina. 

There is also an arrangement in the eye by which it 
adapts itself to different distances in looking at objects. If 
we look through a telescope at a near object, and then turn 
it towards one at a distance, we can not see the latter dis- 
tinctly until we adjust the lenses to suit the distance. But 
in the eye how quickly the adjustment is made ! It is done, 
ordinarily, without any conscious effort on our part. We 
look at an object at a few inches distance, and in an instant 
turn the eye and see an object afar off with almost equal 
distinctness. There has been much discussion in regard to 
the means by which this adjustment is effected, but the 
probability is that, as the lens is very elastic, it is kept in a 
state of tension by the elasticity of the suspensory ligament, 
and consequently is somewhat flattened. Now, if the ciliary 



THE EYE. 



239 



muscle contracts, it will draw the ligaments away from the 
lens, or diminish the elastic tension on the lens. The 
lens, consequently, will become more convex, but will return 
to its former shape, when the ciliary muscle ceases to 
contract. 

331. Difficult)/ in the Near-sighted* — In some 
cases this power of adjustment is counteracted by defect 
is the structure of the eye. Thus, in the near-sighted, 
either the cornea or the crystalline lens, or both, are too 
convex : or, the crystalline lens is too far from the retina. 
The result is, that the rays of light coming from a distant 
object come to a focus before they reach the retina, as rep- 
resented in Fig. 148. All objects, therefore, are seen indis- 

Fig. 148. 




tinctly except those which are brought near to the eye. 
This defect is remedied by the use of a concave lens, which 
counteracts the effect of the too highly refractive power of 
the eye by making the rays divergent, instead of parallel, 
before entering the eye. 

332. The Far-si f/hted.— In the far-sighted the 
difficulty is of an opposite character. The refractive power 

Fig. 149 




of the eye is too feeble. This is owing either to too little 
convexity of the cornea or of the crystalline lens, or of 



240 



PHYSIOLOGY AND HYGIENE. 



both ; or, to too great nearness of the crystalline lens to the 
retina. In this case the rays coming from a near object do 
not come to a focus soon enough. The focus of the rays 
coming from any point of the object is behind the retina, 
as seen in Fig. 149, in which the rays from two points are 
represented as prolonged till they meet. This defect is 
palliated by the use of convex glasses. 

333. Correspondence of Action between the 
two Eyes. — It is an interesting and wonderful fact, that 
as we look at an object with both eyes, although there are 
two images formed, and therefore two impressions carried 
to the brain by the two nerves, yet but a single impression 
is produced in the mind. To produce this it is manifest 
that there must be a very exact correspondence in the two 
eyes as optical instruments. The two images must be simi- 
lar, and must be formed on corresponding parts of the 
retina in both eyes. # 

Thus, if there be a range of objects, as at A, B, C, m Fig. 
150, the impression of each will be a single one in the mind, 

Fig. 150. 




because the picture of each of these objects is on the same 
part of the retina in both eyes, a, &, c, and a', 5', c'. But if 
you press with your finger one of the eyes a little out of its 
place, all these objects will appear double, because their 
images will occupy different parts of the retina in the two 
eyes. 



THE EYE. 241 

334. The Tiro Images of an Object in the 
Tiro Eyes not Exactly Alike.— While it is necessary 
to single vision when both eyes are used, that the image of 
the object should occupy corresponding portions of the 
retina in the two eyes, it is not true that these two images 
are exactly alike. You can verify this by a simple experi- 
ment. If you hold a book before your eyes, with its back 
towards you and in a vertical direction, you see the back of 
the book and its sides at once, as a single object. If now, 
still holding the book in the same position, you shut one 
eye, you see but one side of the cover of the book — that one 
which is on the same side with the open eye. And so with 
the other eye. The plain inference is, that when you look 
at the book with both eyes, the image formed in the right 
eye is composed of the back of the book and the cover of 
the right side, while the image in the left eye is composed 
of the back of the book and the cover of the left side. 
From these two distinct images, two distinct impressions 
are sent to the brain ; and yet but a single impression is 
recognized there by the mind, for the book is seen as a single 
object. This single impression must, therefore, result in 
some way from a mingling of the two impressions trans- 
mitted along the two optic nerves. 

The statements in the last paragraph are beautifully 
illustrated by the instrument contrived by Professor Wheat- 
stone, which he calls the stereoscope. In using this instru- 
ment, you look at two pictures of the same object with the 
two eyes, and yet you see but one thing — that is, but one 
impression is produced in the mind, although two different 
pictures are made in the two eyes, and of course two differ- 
ent impressions are conveyed to the brain. 

Thus, the two representations of a dog, seen in Fig. 151, 

i in the instrument a- ;t single dog. You observe 

that they are shaded differently. They are representations 

the tw«> pictures, which a dog in this position would 

make on the retina in both of the eyes of a person looking 

him. When you look at them in the instrument, the 

single dog that you Bee stands out more than either of the 

11 



242 PHYSIOLOGY AND HYGIENE. 

two representations, as seen when they are not in the instru- 
ment. The reason is obvious. In the two images formed 
in the eyes, as you look into the instrument, are all the 
lines of light and shade which you would see in looking 

Fig. 151. 




at a real dog with both eyes ; while either one of these 
representations contains only a part of these lines. 

335. Rude Imitation of the Stereoscope.— Yom 

can imitate in some good degree the effect of the stereoscope, 
by placing the end of a small book between these figures, 
and letting the other end rest against the nose and forehead, 
thus separating the eyes from each other. If now you look 
intently at the two figures, you will in a few moments find 
them approximate each other, till at length they mingle 
together, and you will see but a single dog, standing out 
like a statue. 

336. Visual Angle. — Let us look now at the means 
by which we gain the experience that is necessary to correct 
vision. One means is the appreciation of the space occupied 
by objects in the field of vision. This is measured by what 
is termed the visual angle — that is, the angle which is 
formed by two lines coming from the extremities of an ob- 



THE EYE. 



243 



ject, and meeting in the eye, as represented in Fig. 152. In 
this way we get the idea of magnitude. 



Fic T . 152. 




But it is manifest that it alone can not give us this idea 
correctly. It would do so, if all objects were at equal 
distances from the eye. But if they are at different distances, 
something evidently must be known of those distances, to 
estimate the magnitude of the objects by the visual angle, 
which they subtend. The arrow at A B will appear just as 
large as the larger one at A' B', because it will occupy the 
same space a b on the retina, and subtend the same angle. 
But if it is known that the one is nearer to you than the 
other, allowance is made for this in the estimation of the 
size. 

The hand, held up to keep the rays of the sun from the 
. would look as large as the sun itself, if one did not 
kn<»w how near it is; and the sun and moon appear to us 
to have about the same magnitude, because we do not fully 
realize the fact that the sun is ninety-two millions of miles 
from us, while the moon is only two hundred and forty 
thousand. 

337* Distance of Objects Estimated by their 

Distinctness.— Another means which we use in getting 

erect idea of objects by vision, is the degree of distinct- 

- in their lines, and shadows, and colors. The fael is 

learned very early by the child, that the nearer objects are, 

the greater is their distinctness ; and he makes use of this 

continually in estimating both their distance and their 

gnitude. By this means, however, he estimates the latter 

. than he does the former. 



244 PHYSIOLOGY AND HYGIENE. 

He makes use of his notion of its distance gained, by its 
degree of distinctness. Many mistakes are made in the use of 
this means of judging the distance of objects. Thus, a very 
bright light will often appear to be nearer than one that is 
less bright. When the atmosphere is very clear, mountains 
and other objects appear nearer to us than they do when the 
atmosphere is thick and hazy. 

338. Size of Objects Estimated by Com- 
parison. — Another means of making a correct estimate 
of the distance and magnitude of objects is, comparison 
with other objects which are familiar to us. Thus, we get 
our ideas of the size of animals from objects in their neigh- 
borhood. The artist makes use of this means of communi- 
cating ideas of size. Figures of men are placed near large 
buildings for this purpose. A notion of the great size of 
the elephant is given by placing his keeper at his side. We 
are not ordinarily aware how dependent we are upon such 
comparisons, in estimating the magnitude of objects. For 
example, a person upon a giddy height suddenly turned his 
eye upon some huts below at a river's side ; they appeared 
to be dog- kennels, till a man issued from the door of one of 
them, and thus, by affording a means of comparison, dis- 
pelled the illusion. 

339. All Images on tike Retina do not Pro- 
duce Impressions in the Mind. — When it is said 
that images of objects are formed upon the retina, and that 
impressions are transmitted from them to the brain, this is 
far from stating all that is true on this point. Many of the 
images pictured upon the retina do not transmit impressions 
to the mind. The sensation of seeing is, therefore, in rela- 
tion to them incomplete — only the beginning of the process 
is effected. - 

This can be verified by a simple experiment. If you hold 
a finger near the eyes (at some ten or twelve inches from 
them), and a finger of the other hand at a greater distance, 
but in the same direction, and then look at the near finger, 
you will perceive that the other finger appears double. So, 
on the other hand, if you look at the distant finger, the 



THE EYE. 



245 



Fig. 153. 



■ ■::"'■ 

■a ... | : 

BE 1 


l^S 


n 


• 

;■ wM ■ 

fig .'.; '. 


1 

1 m 

■ 






• 


! '- m . 

















near one appears double. The reason of this can be made 
clear to you by Fig. 153. The two eyes, L and R, being 
directed so that their axes 
converge on the object A, the 
middle points of the two 
images correspond with the 
middle points of the retina in 
the two eyes, a and a . 

The images thus correspond- 
ing in their place on the 
retina, the impressions carried 
from them by the two optic 
nerves to the brain correspond 
also, and so the vision is single. 
But the image of the object B 
is formed in the two eyes, in 
parts of the retina that do not 
correspond, i and b. They 
are both on the inside of the 
middle points, a a , that is, to- 
wards the nose; whereas the outw r ard part of the retina in 
one eye corresponds with the inward part in the other eye, 
and vice versa. 

340. The "Blind Sj)Ot."—The sensibility of the 
different parts of the retina to light varies greatly. The 
point of entrance of the optic nerve is not sensitive to light, 
as may be proved by a very simple experiment. Close the 
left eye, and look steadily with the right at the letter A on 
the page, held at a distance ten or twelve inches. 

A B 

The letter B will be seen quite plainly, as w T ell as the 
letter A. Xow, move the book slowly toward the eye, which 
must be kept steadily fixed upon the letter A. At a 
certain point the letter B will disappear, but aa the book 
ii brought still closer it will again come into view. This 
Its from the fact that, in the first position of the book, 
the image of the letter B falls between that of the letter A 
and the entrance of the optic nerve; while, in the second 



246 PHYSIOLOGY AND HYGIENE. 

position, it falls on the entrance of the optic nerve itself ; and 
in the third, inside that point. So long as the image of the 
letter rests upon the entrance of the optic nerve it is not 
perceived, and hence this region of the retina is called the 
blind spot. 

341. Defenses of the Eye. — The means by which 
so delicate an organ as the eye is protected from injury, are 
worthy of notice. Observe first its situation. Parapets 
of bone surround it, and receive most of the blows that 
come upon that part of the face. Above is the strong 
arch of bone, forming the lower part of the forehead. 
Then there are the cheek bones, and the bones of the 
nose. Thus, walled in, in all directions, by these prom- 
inences, the eye is seldom hurt, except by a direct thrust. 

And besides being thus protected by surrounding bones, 
it reposes upon a soft cushion of fat, which yields, if the 
eye be pushed backward by violence. Indeed it is pushed 
backward effectually by the muscle that closes the eyelids 
whenever an impending blow is anticipated, and it is thus 
sunk farther back in its cushioned recess, amid the pro- 
jecting parapets, and of course receives less of the force of 
the blow than it otherwise would. This muscle, also, by 
its instantaneous action, prevents many light particles from 
flying into the eye. Such particles are also often prevented 
from entering the eye, by being intercepted by the eye- 
lashes. 

The eyelroiv, besides being an ornament, protects the eye 
from harm, by preventing the salt perspiration from run- 
ning down into the eye, and irritating it. It acts as a 
thatched roof, projecting from the arch over the eye, and 
letting the perspiration from the forehead evaporate from 
it. The eyelashes also serve to keep the perspiration of the 
eyelids from entering the eye. 

The structure of the eyelids is such, that the freest mo- 
tion is allowed, while they afford by their firmness consid- 
erable protection to the organ. They derive their firmness 
from a fibrous cartilage, which makes the body of each lid. 
You can readily see that this cartilage, making an even 



Tin: eye. 



•m; 



Fig. 154. 



pressure on the surface of the eye, must often prove an 
effectual defense against direct thrusts. U the weapon hit 
this cartilage, it aers as a firm shield, to ward off the blow 
from the eye behind it. 

And even that part of the lid which is intended by its 
laxness to allow free motion to the lid, the skin, is often 
an effectual defense. If an impending blow be seen, and 
the eye he instantaneously and forcibly shut, the wrinkled 
skin forms a soft cushion over the eye. and thus not only 
ers it up, but serves materially to deaden the force of 
the blow. 

342. Tear Apparatus.— The tear apparatus affords 
the eye material protection. The bland tears keep the 
organ properly lubricated, 
uit its constant motions 
occasion no irritation. And 
if any thing gets into the 
the tears are manufac- 
tured abundantly, for the 
purpose of washing out the 
intruding substance. Fishes 
have no need of a tear ap- 
paratus, as their eyes are 
washed constantly by the 
water in which they live. 

In Fig. 154 is represented 
the tear apparatus. The 
■reted by a small 
gland, called the lachrymal 
glands Bituated at a, in the 
orbit under the arch of the forehead, and near the outer 
angle of the eye. At b are the ducts which empty the tears 
in upon the surface of the eve on the inside of the upper 
lid. 

By the constant motions of the organs the tears are dif- 

hole surface, and thus continually wash the 

rrangemenl for carrying oil' the fluid is this. 

It flows through a tube, d, '. into the nose This tube has 




TEAR APPARATUS. 



248 PHYSIOLOGY AND HYGIENE. 

at its beginning in the eye two branches, c, c, which open 
on the edges of the two lids at the inner corner of the eye. 
These open mouths, that drink up the tears as they flow 
to them, you can very readily see. The drain of the eye, 
which thus conveys the lachrymal fluid to the nose, is ordi- 
narily capable of taking care of all the tears made by the 
gland. 

But when an uncommon amount is made, as in weeping, 
it cannot receive all the tears, and they therefore overflow 
their banks, the edges of the eyelids. And sometimes there 
is a constant overflow from obstruction of the drain by 
disease. The continual weeping of the eye, when this ob- 
struction exists, will give you some idea of the amount of 
fluid which the lachrymal glands make. 

343. Oiling the Eyelashes. — Along on the edge 
of each eyelid are some very small glands which secrete an 
oily substance. This serves two purposes. It oils the eye- 
lashes, and also prevents the tears, when they are only in 
ordinary quantity, from being diffused over the edges of the 
eyelids in the constant motions of the eye. 

This exceedingly small quantity of oily substance suffices 
to keep the tears in the eye where they are needed. There 
is also a curious provision for directing the tears to the 
mouths of the ducts when the lids are 
closed. When brought together their edges 
unite in such a manner as to form with 
the surface of the eye a triangular chan- 
nel for the tears to run in. This is made 
clear by the diagram in Fig. 155, in which 
the line i represents the surface of the eye, 
and a the edges of the lids, showing a sec- 
tion of the canal between them. 

344. Nietitating Membrane in 
the Eyes of Birds. — We had intended 
to notice some of the peculiarities of the eyes of different 
classes of animals. We will, however, notice but one — the 
nictitating membrane in the eyes of birds. When not in 
use it is gathered up in the inner corner of the eye. When 




HYGIENE. 



249 



it is stretched over the organ we see that it is a thin trans- 



that 



as soon as 



Fig. 156. 




lucent membrane. It is very elastic, so 
the muscles sweep it quickly over the 
eve, it flies back at once to the corner 
where it is so snugly folded. In Fig. 156 
it is represented as half way over the 
front of the eye. In Fig. 157 are seen 
ihe curiously arranged muscles that move 
it. One of the muscles, g, arises from the 
ball of the eye at its upper part, and 
running back, forms the trunk of the 
optic nerve, a tendon with a loop, through 
which the tendon of the other muscle, p, 
works. 

This muscle arises from the lower part 
of the ball of the eye, opposite to the 
origin of the first muscle. Its tendon, t, 
is fastened into the edge of the nictita- 
ting membrane. It acts through the loop 
as a pulley, and you can see that the 
muscle, g, assists it materially in effecting the very quick 
motions of the membrane. 



Fig. 157. 




CHAPTER XVI 

HYGIENE, 



After having considered the construction of the machin- 
of the human system and the uses which the mind 
makes of it, one naturally inquired what the conditions 
"ii which depend the full development of this com- 
plicated machinery and its daily repair? 

34£. Sources of our 'Knowledge of Hygiene* 

— The principles and rules of Hygiene are to be learned 



250 PHYSIOLOGY AND HYGIENE. 

from two sources. 1. They are to be learned from Physi- 
ology. As we observe the functions of the different organs, 
we can learn what those circumstances are which favor their 
due performance, and what those are which interfere with 
it. 2. They are to be learned, also, by observing the effects 
of those agencies which are known to interfere with the 
functions and to produce disease. 

An exemplification of these two modes of learning the. 
principles of Hygiene in relation to a single point will 
suffice. The study of the physiology of the chest shows us 
that nature has, in the construction of its framework, 
especially provided for giving ample room to the lungs ; 
and so we deduce a law of Hygiene, that the chest should 
not in any way suffer compression. This is the first mode. 
But the same law can be deduced by the second mode, that 
is, by observing the results of compression of the chest. 

Eules of hygiene generally have but little practical influ- 
ence, unless the physiological facts upon which they are 
based are understood. Although the evil effects of their 
violation may be vividly portrayed, and even illustrated, as 
in the case of the chest, by engravings, the impression upon 
the mind is by no means so thorough and practical, as 
when the same lesson is enforced by a clear knowledge 
of the functions and arrangements of the organs and the 
conditions necessary to their healthy action. Physiology, 
therefore, should be studied as preparatory to a proper 
appreciation of Hygiene. 

Not only is a knowledge of Physiology essential to a 
proper appreciation of the rules of Hygiene, but in many 
cases they cannot be fully understood in their varied appli- 
cation without such a knowledge. With the very partial 
and superficial knowledge of Physiology that is usually 
communicated with Hygiene, these rules are for the most 
part merely arbitrary. And just so far as the principles 
on which they are based are not understood, is there a 
liability to mistake their application. 

In considering the subject of hygiene, the natural divi- 
sion of Physiology should be kept in mind. There is a 



HYGIEN1.. 251 

hygiene relating to the construction of the machinery of the 

body, and there is also a hygiene relating to the uses of this 
machinery. Besides, each organ lias, to a certain extent, its 
own hygiene. And yet, as all the organs are more or less 
connected in sympathetic action, there is a general hygiene 
of the system. 

346. Hygiene of Digestion. — Many of the points 
in the hygiene of the digestive organs have been already 
noticed in the physiology of digestion. Nothing more is 
needed in addition to what is said there of the importance 
of the thorough mastication of food, and of its having a 
due amount of saliva mingled with it ; of the evils result- 
ing from eating too fast, from eating between meals, and 
from eating a great variety of food; and of the influence 
of exercise upon the process of digestion. There are some 
other points, however, that remain to be noticed. 

347* Quantity of Food to be JEaten. — No very 
precise rules can be given as to the quantity of food that is 
proper to be eaten. But a consideration of the physiologi- 
cal principles of digestion suggests rules that are sufficiently 
definite for practical purposes. There must be such an 
amount of food as will furnish sufficient chyle to keep the 
blood, the building material of the body, in proper quantity. 
The question arises, how shall we know what amount of 
food is requisite for this purpose^ 

rtunatcly, the want of the system -and its supply are 
commonly quite accurately indicated by the sensations. 
The proper hygienic rule then on this point is, that we 
should cease to eat when the sensations created by the want 
of the system are removed — that is, when the hunger is 
appeased, and the accompanying feeling of discomfort is 
BUCCeeded by a feeling <>f agreeable ease. 

348. Mistakes as to Quantity of Food. — But 

mistake- often made in regard to these sensations. 

They may be prevented from making a true report. Thus, 

when eating U done too rapidly, more food than is needed 

introduced into the stoniaeh before t he sensat ion 

of ease and satisfaction is experienced. It is only when 



252 PHYSIOLOGY AKD HYGIENE. 

suitable time is given to mastication, and the food is rather 
gradually introduced, that this sensation indicates the proper 
limit of eating. 

Again, there is a very common mistake in regarding the 
feeling of fulness instead of the sensation alluded to, as indi- 
cating the time for ceasing to eat. Those who adopt this 
false rule generally make the stomach bear as much as it 
can without absolute discomfort, and many daily overreach 
this point. The result is, that this organ soon gives out 
under this daily overworking; or, if the stomach be a strong 
one, an injurious repletion is produced in the system. 

Too little food is sometimes taken. Poverty is commonly 
the cause. But sometimes it arises from false notions; as, 
for example, the notion that the quantity of food should be 
regulated by weight, or the more common notion, that we 
should rise from a meal with some appetite remaining. 
The result is, that there is not a sufficient supply of chyle 
to meet the wants of the system. The wear and tear create 
a demand which is greater than the supply, and the body 
therefore loses its fulness and its vigor. 

349. Length of Intervals between Meals. — In 
determining the length of the intervals between the meals, 
we should have regard to the time required for the comple- 
tion of the process of digestion, and to the wants of the 
system. Some articles are digested more rapidly than others, 
but it commonly requires 'from three to four hours to com- 
plete the digestion of a meal. When the system is in a state 
of action, its want of food, as indicated by its sensations, 
shows itself a little time after the completion of the process 
of digestion. The interval, then, between the meals should 
not vary much from five to six hours. If it be made 
longer, some degree of exhaustion results ; and if it be less, 
disturbance of the digestive process may occur, from having 
the digestion of one meal begin before that of the previous 
one is fairly finished. 

350. JHer/ularity of Meals. — It is important that 
the meals should be eaten at regular periods from day 
to day. For the stomach, with its times of work and of 



HYGIEXE. 253 

rest, naturally contracts regular habits, a disturbance of 
which is injurious. This obedience to habit in this organ 
is manifest whenever any change is made in the time of 
eating. 

351* Quality of Food. — The question is often asked, 
whether such and such an article " is healthy," as if there 
were essentially different degrees of suitableness in different 
articles of diet So far as digestion is concerned, any article 
is healthy for any individual whose stomach can digest it 
without difficulty. An article may be perfectly healthy for 
one, and unhealthy for another. There are sometimes wide 
differences in this respect, owing to unaccountable peculiari- 
ties. But even in regard to ordinary differences, the question 
as to the propriety of any article of food is wholly an indi- 
vidual question. 

Our food should be varied in the different seasons of the 
year to a greater extent than is common. In the warmer 
seasons it needs to be less stimulating, less heat-producing 
than in the colder seasons. The fruits, each in its season, 
should, in the warmer months, regularly form quite a large 
proportion of our food. If used thus, they will tend to 
prevent, rather than induce, the complaints peculiar to that 
portion of the year. 

352. Influence of the Mind on Dir/estion. — 
The state of the mind has much influence on the digestive 
organs. This is sometimes strikingly exhibited in the loss 
of appetite on the sudden reception of bad news. It is also 

. in the influence of continued sorrow upon the appetite 
and the digestion. It is not strange, then, that one of the 
prominent causes of dyspepsia is mental disturbance or de- 

arion. And a cheerful mind is very properly deemed to 
be essential to easy and thorough digestion. 

353. Hygiene of Respiration. — In order to un- 
derstand fully the hygiene of respiration, it must lx) borne 
in mind, that the great objeel of this function is to bring 

tir into all the minute air-eells of the lungs, that it may 
change the blood which is sent there for this purp 
Anything, then, which interferes with the free introduction 



254 PHYSIOLOGY AND HYGIENE. 



of the air into these cells is a palpable violation of the law: 
of health. And yet this interference is so commonly prac- 
tised, that it is one of the prominent causes of disease. 

354. Compression of the Chest.— This interfer- 
ence is effected in two ways. It is done, first, by mechanical 
compression of the chest. Although, as shown in the 
Chapter on the Kespiration, there are special pains taken 
by the Framer of our bodies to provide, in the construction 
of the chest, for the free introduction of air into the lungs 
under all circumstances, this is often prevented by certain 
prevalent modes of dress. 

It must be observed that in the arrangement of the chest, 
a free motion of its walls in the expansion of the lungs is 
contemplated. The dress, therefore, should always be so 
loose as to admit of this free motion. If it is not, the air 
is not freely admitted to all the air-cells, and therefore the 
blood is not so fully changed, as nature requires ; and the 
health is impaired just in proportion to the degree in which 
the due expansion of the chest is prevented. 

Compression not only produces disease in the lungs, but, 
by preventing these organs from effecting fully the requisite 
change in the blood, it impairs the quality and lessens the 
quantity of this building material, and thus diminishes the 
nutrition and the vigor of the system, and therefore renders 
it liable to a great variety of diseases, especially those of 
which debility is a prominent characteristic. 

355. Importanee of a Good Supply of Pure 
Air. — The free introduction of pure air into the lungs is 
interfered with, secondly, by cutting off its supply. As you 
learned in the Chapter on Kespiration, the oxygen of the 
air is used up in large quantities by the lungs, and the car- 
bonic acid gas thrown off takes it place. If, therefore, 
there be not sufficient provision for the supply of fresh 
relays of pure air, a mixture of air and carbonic acid gas 
will be introduced into the lungs at every breath, so that 
there will not be sufficient oxygen to effect thoroughly the 
change in the blood. 

In this respect, therefore, the result is the same as when 






s 

: 



HYGIENE. 255 

too little air is admitted by reason of compression of the 

chest. A portion of the requisite quantity of pure air is 
shut out, in one case by diminishing the capacity of the 
chest, and in the other by. having the lungs in part occupied 
by carbonic acid gas. 

356* Bad Results of Defective Aeration 
Seldom Appreciated. — The influence which this defec- 
tive aeration of the blood, occasioned by these two causes, 
exerts upon the health, is seldom appreciated. For unless 
the deficiency be very great, no immediate obvious result is 
produced. But though the deficiency may be comparatively 
small, if it be continued from day to day for a long time, 
the aggregate result of this steady depressing influence is a 
serious one. 

The destruction of health and of life that comes from 
this imperceptible agency in every community is vast in 
amount. But most persons seem to be insensible to this 
fact. They need a narrative of such a destruction of life as 
occurred in the Black Hole at Calcutta, to convince them 
that a considerable quantity of fresh air is required by every 
pair of lungs. And it is only by a description of an exam- 
ination after death of some one who has been killed out- 
right by extreme compression of the chest, that they can be 
made sensible of the need that the lungs have of the room 
that nature has given them. And even then the impres- 
sion seems to be a momentary one. 

If all the injury that is done by defective aeration of the 
blood could be visibly traced out, we should then realize the 
necessity of having just as many of the air-cells, those little 
chemical laboratories, as nature designed, and of keeping 
them well supplied with the fresh air which they require 
for the life-giving work that they perform. 

357. Hygiene of the Circulation. — The hygiene 
of the circulation need not detain us long. The office oi 
the organs of the circulation is to circulate the blood, the 
building material, everywhere. They never rest from their 
work. But they work more actively when the muscular 
in ifi in action than when it is at rest. As one lies in 



256 PHYSIOLOGY AND HYGIENE. 

bed, the circulation goes on steadily, but quietly. But on 
rising and moving about, the circulation becomes more 
active. Not only does the heart beat more quickly, but the 
capillaries in every part of the body increase their action. 
And, as more blood is carried to every part, there is more 
done everywhere. We see this in the skin, in the increase 
of the perspiration on exercise. When the muscular effort 
is very great, the excitement of the circulation is violent and 
tumultuous. The heart beats strongly and rapidly, and the 
flushed face shows how active is the circulation in its ex- 
treme vessels, the capillaries. 

358. Exercise Necessary to Health. — The occa- 
sional excitement of active exercise is absolutely essential to 
the proper physical development. The body may sometimes, 
indeed, maintain its proper bulk in a continued state of 
muscular inaction; but its textures will not have the requi- 
site strength and tone. That they may have these qualities, 
it is necessary that the blood be often pumped into their 
capillaries with the force that is given to the heart by active 
exercise. 

It is not the muscles alone that are rendered stronger and 
firmer by exercise, but the same effect is produced in all the 
textures, the bones, the ligaments, the veins, the skin, &c. 
The great internal organs of the body are firmer, more tit to 
perform their duty, and less liable to disease, if the circula- 
tion in them is excited daily by this means. Active exercise 
makes the stomach digest better, the lungs perform the work 
of aerating the blood more thoroughly, and the brain serve 
the mind more easily and effectually ; it therefore renders 
one less liable to dyspepsia, to consumption and other dis- 
eases of the lungs, and to apoplexy and other diseases of 
the brain and the nervous system. 

But the activity of the circulation may be made so violent 
by exercise as to do some damage. Though its organs are 
capable of bearing much in this respect, there is some need 
of caution. Harm is undoubtedly often done in trials of 
strength when the effort is both violent and prolonged. 
Vigorous action answers fully the purpose of developing 



HYGIENE. 257 

power and firmness; but violent action is attended with 
some hazard. 
lioi). Hygiene of Formation and Repair — 

In considering the hygiene of formation and repair, it must 
be borne in mind that there is constant change everywhere 
in the system. Particles that have become useless in the 
textures are continually taken up and carried away in the 
veins or the lymphatics, and other particles are put in their 
places, being taken for this purpose from the blood in the 
capillaries. This change is going on during all the period 
of growth, as well as afterwards. The health and vigor of 
the textures, and therefore of the system as a whole, are de- 
pendent upon the proper performance of this constant pro- 
i >f removal and fresh supply. 

There are two conditions necessary to the due perform- 
ance of this process. The first is, that the blood, the uni- 
versal material for building and repairing, shall be of good 
quality. This is secured when the digestive process, which 
furnishes the blood, is well performed, and the lungs and 
other organs, that purify the blood by discharging its refuse 
matter, are in good condition. The second condition is, 
that the blood shall be often quickened in its course through 
the organs by the excitement of exercise. This has been 
mentioned in speaking of the hygiene of the circulation. 

liiiO. Necessity of a Free Discharge of the 
Waste. — The necessity of having the waste matter that is 
brought back from all parts of the body in the venous blood, 
effectually discharged by the various organs designed for this 
purpose, requires a particular notice. The lungs, the skin, 
the liver, the kidneys, &c, must thoroughly evacuate this 
waste, or its retention will impair the quality of the blood, 
and thus interfere with the proper nutrition of the body, or, 
in other words, with the process of formation and repair. 
And the retention of this refuse in any considerable amount 
■ mediately productive of disease. 

The lungs, while they take in oxygen from the air, dis- 
charge carbonic acid gas, that pari of the waste of which it 
is their duty to rid .the ostein. If this carbon bo retained, 



258 PHYSIOLOGY AND HYGIENE. 

the blood is impure in proportion to the degree of reten- 
tion. 

361. Functions of the Skin. — It is the duty of 
the skin to discharge some portion of the refuse of the sys- 
tem in the sensible and insensible perspiration. The skin is 
not a mere covering of the body, but it is also an active 
organ, performing very important functions. It continually 
discharges through its numberless pores a large quantity of 
matter. 

Although this matter is mostly in an insensible form, if 
from inactivity of this organ it fail to be discharged, its reten- 
tion renders the blood impure, and so does injury to the sys- 
tem. At least two pounds of matter are discharged from the 
skin in twenty- four hours. This being the case, it is not at all 
wonderful that activity of this organ should be so necessary 
to health, and that the suspension of its secretions should 
have so much influence in the production of disease. 

362. Animal Heat.— In the Chapter on Eespiration 
you learned that the heat of the body is produced by the 
change that takes place in the blood in the capillaries, as 
it receives the waste particles, and as the new are deposited 
in their places. This change makes a real combustion in 
every capillary. The more rapid therefore is the change 
the greater is the combustion, and of course, the greater is 
the heat. Hence comes the increased heat of exercise. 

Exercise makes more w r ear and tear, and so disengages in 
the waste more carbon and hydrogen to unite with the in- 
creased amount of oxygen that comes in the quickly flowing 
blood to the capillaries ; and just as in combustion that is 
attended with flame, the greater the amount of fuel the 
greater is the heat. We have a familiar example of the pro- 
duction of heat by exciting the circulation, in the ex- 
pedient often resorted to by laborers for warming the 
hands, of striking them with a swinging motion upon the 
shoulders. 

The amount of heat produced in the body depends also 
on the quality of the blood. The richer it is, the more oxy- 
gen it contains, and therefore, the brisker is the fire in the 



HYGIENE. 259 

capillaries, and the greater is the heat. You see then why 
it is that those who have a good state of the blood, and ex- 
se much, maintain the heat of the system better, and so 
need less clothing than those whose blood is weak, and who 
exercise but little. 

The heat of the body is maintained in all temperatures 
of the atmosphere very nearly at 98° Fahrenheit. This is, 
yen observe, much above even the highest temperature 
that is agreeable to us. You see then that it is essential 
to the comfort of the body that it be giving off heat con- 
tinually to the surrounding atmosphere. It the atmosphere 
be at 98°, the same temperature with the body, there is 
great discomfort, from the fact that the heat is given off 
-lowly. 

It would not be parted with at all if the skin were not an 
active organ. It is by the evaporation of the perspiration 
thrown off by the skin that the extra heat is got rid of wiien 
the air is so hot. The temperature in which the body is 
generally most comfortable is about 70°. AVhen the atmos- 
phere goes below this, we need the ordinary expedients to 
prevent a too rapid escape of the heat from the body. 
The clothing and the heated air, with which we surround 
ourselves to guard against the cold, do not act by com- 
municating heat to the body, but simply by retarding its 

I ,e - 
Cold is a depressing agent, and exerts as such much in- 
fluence in the production of disease. Statistics show this 
in a striking manner. The statistics of London, for ex- 
ample, prove that the mortality of a severe winter is much 
than that of a mild one. And this difference Is 
bund to be chiefly among the very young and very old, 
in them the power of generating heat is feebler 
than in other class 3. 

Tl r is this heat-producing power of the system, 

the better do the depressing influence of 

cold. Ail those means, therefore, which promote the vigor 

of the body 9 oxe the be.^r of tie- safeguards t<» be used againd 

productive caug ad death. But, besides 



260 PHYSIOLOGY AND HYGIENE. 

thus fortifying the body internally against this depressing 
agent, we have the means of outer defence alluded to, 
in clothing and heated air. As there are many errors 
committed in using these, they require a more particular 
notice. 

Clothing serves, as has been said, to shut in partially the 
heat which is generated in the body. Its amount and char- 
acter should be regulated by two circumstances — the degree 
of the cold, and the amount of heat-generating power in the 
system. The vigorous require less clothing than the weak, 
because they have more of this power ; so, also, the body 
needs less clothing when it is in exercise than when it is in 
a state of rest, because in exercise it generates more heat. 
And the same principles apply to heated air, for this is an 
outer covering for the body, interposed between it and the 
cold, like clothing, for the purpose of preventing the too 
rapid escape of the heat generated within. 

These plain principles are violated in various ways. Many, 
from carelessness or from mistaken notions, are often un- 
necessarily exposed to the depressing influence of cold. 
They are not sufficiently aware of the necessity of guarding 
so much more thoroughly against the cold when at rest than 
tvhen exercising. And then, on the other hand, they add to 
the effect by having too much clothing when in action, or 
when in a warm place. When they thus suffer first from 
too much heat, an after exposure to cold is exceedingly in- 
jurious. 

The weak especially suffer from exposure to cold when 
the body is at rest, and therefore, they should take special 
pains to guard themselves against this depressing agent. 
Any attempt on their part to harden themselves, as it is 
expressed, by making use of as little clothing as the vigor- 
ous wear, particularly when the body is in a state of inac- 
tion, always does harm. 

The very thin coverings so commonly seen on the feet 
of delicate females are palpably inconsistent with this rule 
of hygiene, and are in ridiculous contrast with the stout 
coverings considered necessary for the feet of vigorous men. 



HYGIENE. 261 

363. Cold Sometimes a Stimulant.— The de- 
pressing influence of cold sometimes produces a marked 
immediate effect. But this is not generally the case. Com- 
monly no harm is apparently done at the time, and so little 

. is thought of it. But if this influence be continued day 
after day, its effects accumulate and become established. 
The vigor of the system is more or less destroyed, and some 
local disease may make its appearance. The debilitating 
influence of cold is in this way a fruitful cause of disease, 
not only in the abodes of poverty, but even among those 
who have ample means of guarding against it. 

Although cold is generally a depressing agent, it is often 
indirectly a stimulating one. It is so when, in consequence 
of its impression upon the skin, it excites what is termed a 
reaction. Several circumstances are necessary to this result. 

1. There must be the power of reaction in the system. There 
may be so much debility that reaction can not be awakened. 

2. If the system be in a state of rest, the application of cold 
must be temporary. A continuous application of it would 
be depressing, and would forbid reaction. 3. In an active 
state of the body, reaction may be produced even when the 
application is continuous. Thus the mere exercise of dress- 
ing may suffice to awaken reaction in a degree of tempera- 
ture which would chill one through if he were sitting still. 

364. Conditions oh which Reaction De- 
pends. — The system may be accustomed to react under 
the impression of cold in two ways. 1. By exercise in the 

n air in cold weather. Those who have but little out- 
door exercise in cold weather, have but little power of re- 
action, and therefore feel the depressing influence of the 
cold whenever they are exposed to it. 2. By a judicious use 
of cold bathing. The object of cold bathing, aside from 
purposes <»f cleanliness, is to accustom the system to react 
under the influence of cold. It is only wdien reaction occurs 
under it- use that it does good. It does positive harm when 

non does not occur: and the harm done in this way 
day after day. by depressing the vital powers, is sometimes 
at length ruinous to the health. 



262 PHYSIOLOGY AND HYGIENE. 

365. Cold Bathing. — There is a want of proper dis- 
crimination in many writers on hygiene in regard to cold 
bathing. It is a mistaken ultraism to say, as is often 
said, that the preservation of health requires that the whole 
body should be bathed every day in cold water. Neither 
cleanliness nor the other purpose mentioned ordinarily re- 
quires so frequent and thorough bathing as this. The 
water may be applied to only a part of the body at a time, 
and yet accomplish all that we wish. Indeed, some person 
of delicate constitution can not bathe the whole surface at 
once with cold water. They may at first be able to apply it 
to only a small part of the body. 

But they may, with the aid of friction, after a while come 
to apply it over a considerable portion of the surface, or 
perhaps over the whole. In some persons this extension of 
the limits of the bathing from day to day must be done very 
cautiously ; and there is occasionally one that can not bear 
it at all over any considerable extent of surface. It is 
necessary for some, in accustoming themselves to cold 
bathing, to begin with using tepid water, making it from 
day to day a little colder. 

The best time for cold bathing is commonly in the latter 
part of the forenoon, for the system is then in its most 
vigorous state, and is therefore best prepared to react. But 
in most persons reaction can be secured at the hour of rising, 
and this is the most convenient time for bathing. Few can 
use the cold bath with profit in the latter part of the day, 
for the powers of the system are then more or less exhausted, 
and full reaction is not easy. The soothing influence of the 
warm bath is appropriate at that time. There are many 
other points in regard to bathing that might be noticed, but 
space will not permit it. 

Thus far we have spoken mostly of the hygiene of the 
body as a structure. But digestion, the circulation, &c, are 
engaged in constructing and repairing organs for the use of 
the mind. In this use, there is wear and tear, and hence 
is the necessity of seasons of rest, that the needed daily re- 
pair of the organs may be effectually done. The mind uses 



HYGIENE. 203 

the muscles and bones for motion, the various organs of the 
senses in gaining a knowledge of the world around, and the 
brain in thinking, willing and designing. Any of these 
organs may be overworked, and after a certain amount of 
work has been done, there needs to be an interval of rest 
repair. The repair is going on continually, while the 
organs are at work; but it can not be done thoroughly 
without these intervals of rest. Most of the repairing is 
done in these periods. This simple statement suggests the 
principles of hygiene in regard to the uses which the mind 
makes of the organs of the body. These will now be de- 
veloped briefly in regard to the muscles, the senses, and 
lastly the brain. 

,306. Exercise Necessary to the Development 
of both the Muscles and the other Organs. — 
There is a certain amount of muscular exercise which is 
essential to firm health. While no one can fall below this 
amount without impairing the healthy vigor, the laborer 
3 much beyond it without injury. There is a wide range, 
therefore, in the amounts of muscular exertion that are cou- 
nt with health. 
The exercise of the muscles is necessary to their full de- 
velopment. When a limb fails to be used, as, for example, 
in palsy, the muscles become small and lose their firmness. 
When, on the other hand, the muscles of any part of the 
y are much used, they become more developed than 
others less used. For example, the labor of the blacksmith 
l«»ps the muscles of his arms largely. The same thing 
ic of the muscles of the leg in the rope-dancer. It i< 
only a general exercise of all the muscles of the body that 
lops them in all parts of the frame in their due pro- 
portion. 

But muscular exercise is also necessary to the proper 

dopmenl of the other textures as well as the muscles. 

Th< : illustration of this influence of exercise which 

a a particular notice, a- it serves to prevent 

rmity. In the universal vigor and firmness of the 

textures which free exercise tends to produce, there is 



264 PHYSIOLOGY AND HYGIENE. 

ordinarily a precise equality between the two halves of the 
body : the muscles on the two sides act with equal power ; 
the spinal column, the grand pillar of the trunk, is held 
between the muscles that bind its twenty-four bones to- 
gether with great exactness, and there is a beautiful sym- 
metry in the whole frame. 

But when, from lack of exercise, there is want of firm- 
ness in the textures, this symmetry is apt to be lost during 
the development of the frame, and the spinal column is 
especially apt to become deformed. 

367. Deformity of the Spine. — There are two 
immediate causes of this deformity, viz., irregular muscular 
action, and irregular pressure. Weakened muscles are prone 
to act irregularly ; and structures that have lost their firm- 
ness, readily yield to any pressure that is laid upon them. 
When there is firmness of texture, irregularities of pressure 
are not apt to produce deformity, because the elasticity 
prevents the permanent influence of such pressure. The 
moment the pressure ceases, the elasticity of the part re- 
stores it to its usual shape. The firm regular action of the 
muscles also tends to the same result. 

Thus, in the case of the spinal column, if the posture of 
the body be such that it is bent over to one side for some 
time, the moment that the posture is altered, the elastic 
cartilages resume their usual shape which has been tempo- 
rarily changed by the unusual pressure, and the muscles 
also that lie along this pillar of bones bring them at once 
to their right position. 

But if the cartilages have lost in some measure their 
elasticity and the muscles are weak, the righting up of the 
spinal column is not fully accomplished ; and a succession 
of slight failures in this respect will, after a while, produce 
a permanent deformity in the direction of the most com- 
monly assumed posture. 

You can see all this exemplified if you observe the differ- 
ence between males and females in regard to deformity of 
the spine. This deformity is exceedingly common among 
girls, while it is rare among lads. The simple reason is, 



HYGIENE. 265 

that lads have the invigorating influence of free out-door 
exercise. Too much influence is attributed to posture in 
producing this deformity. Posture is often spoken of as 
being the chief cause of it, and this view of the subject is 
illustrated extensively with cuts, showing how the deform- 
ity is occasioned. 

If this were the correct view, there should be much less 
deformity among girls than among boys in our schools, for 
the former sit in a crooked posture much less than the lat- 
ter do. So far as posture does have an influence, it is quite 
clear that the prim, fixed posture enjoined upon the girl 
has a tendency to produce deformity, by adding to one of 
the causes from which it proceeds, viz., the weakness of the 
muscles. A fixed uniform posture wearies the muscles, but 
variation- of posture relieve them, and so prevent an ex- 
haustion of their power. 

The muscles of the back in the female are weakened, in 
common with the other muscles, not only by a want of stir- 
ring out-door exercise, but also by a special cause of weak- 
ness in their case. The tight dress of the girl prevents 
these muscles from having that free action which the loose 
dress of the boy permits. You can see this in the differ- 
ence of movement in the two cases. In the boy, the spine 
is bent and twisted in all directions freely ; but in the girl, 
both custom and the stiff tightness of the dress require a 
movement almost as if the spine were a single bone, instead 
of being made up of twenty-four bones. The muscles in 
her back, therefore, lose their power and fulness just as the 
unused muscles of a palsied limb do. 

368. Exercise should be Varied and Gen- 
eral. — Variety should be aimed at in the action of the 
muscles. A continuous action of any set of muscles is 
wearisome and painful. This is well exemplified in the 
punishment once much in rogue in schools, of making the 
ider hold a book our al arm's length for Borne time. 
In the management of the muscles of the voice, the weari- 
y continued sameness of action is often experi- 
xL The monotonous speaker or reader tires out thece 
12 



266 PHYSIOLOGY AND HYGIENE. 

muscles much sooner than one who has great variety in his 
tones. 

369. Gymnastics and Calisthenics. — A gen- 
eral exercise of all the muscles is essential both to sym- 
metrical muscular development, and to the full attainment 
of the invigorating effects of exercise. Gymnastics and 
calisthenics are, in this respect, particularly beneficial. 
These are, however, no better than any other exercises that 
are so varied as to bring the muscles generally into action. 

The varied exercises of walking, running, leaping, riding 
on horseback, dancing, and active sports, are quite as good ; 
so also are the varied labors of the garden, if they be 
pursued with interest and pleasure. There is no especial 
benefit in the extreme variety of exercise sometimes aimed 
at in gymnastics. Variety that is sufficient to bring into 
general action the muscles of the body is all that is 
requisite. 

Gymnastics and calisthenics should always be considered 
as subsidiary to the common exercises that have been men- 
tioned, and should never be permitted to exclude them. 
When they are made to do this, a temporary benefit is 
reaped at the expense of a permanent injury. For after 
the novelty of the round of exercises has passed away, they 
are given up, and the common and now despised exercises 
are not apt to be resumed. Habits of inaction, therefore, 
are often confirmed, instead of being removed, by a sys- 
tematic course of exercises under the high-sounding names 
of gymnastics and calisthenics. 

370. Effect of too severe Exercise. — But there 
may be too much exercise. The toil of the laborer may be 
so severe and long-continued, that the reparative process 
in the intervals of rest is not competent to effect a full 
repair of the muscles. A gradual exhaustion of their 
power, therefore, results. Much harm is thus often done 
by severe unremitting toil. Especially is this the case 
when the excess of toil is exacted during the period of 
growth. 

It is necessary that exercise should be agreeable in order 



HYGIENE. 267 

to produce its best cflect on the system, on account of the 
genial excitement which then accompanies it. For this 
m exercise should commonly not be solitary, and there 
should, if possible, be some object- connected with it. If 
the observation of nature were made from the beginning 
of education as prominent as claimed in the Preface that 
it should be, there would be no lack of objects in the ram- 
bles in held and forest taken both for health and for the 
pursuit of science. 

371. Hygiene of the Soiscs. — Substantially what 
has been said of the muscles may be said of the organs of 
the senses. They require intervals of rest for thorough 
repair. And they may be so overworked that complete repa- 
ration is rendered impossible, and their power be gradually 
exhausted. The office of the senses is to receive impressions 
from things around. Whatever gives an impression to any 
organ of sense may be regarded as a stimulus to it. If 
the stimulus be too great or too long continued, injury is 
done. This is very obvious in regard to the eyes. They 
are often injured by too much light. A word of caution 
is needed in regard to the production of near-sightedness. 
This is often caused in students and others by holding ob- 
jects too near the eyes. 

372. Necessity of Seasons of Best to the 
Erain. — We come now to the hygiene of the brain. This 
is the great central organ or instrument of the mind, by 
which it receives the impressions made upon the senses, com- 

- and arranges the knowledge thus gathered, and origi- 
ns those impressions that are made by it upon the world 
around through the action of muscles. It is a very com- 
pound instrument It needs, like the muscles, seasons of 
f<>r the full repair of the wear and tear occasioned in 
rily use. 
I- may be overworked, and then the repair will not 
be complete, and gradual exhaustion of its powers will 
3ioning disease in some form. A significant 
illustration of tin* importance of seasons of res< tor repair 
in t; of the brain is furnished in the fact, that 



268 PHYSIOLOGY AND HYGIENE. 

insanity is not apt to result from mental disturbance, unless 
the subject of it fail to have his regular sleep. If he sleeps 
well, the work of repair is so well done in the brain in its 
nightly seasons of rest, that the disease, which might other- 
wise occur, is prevented. 

With proper intervals of rest, the mind can perform a 
large amount of labor without injury to the brain and 
nervous system, if there be no undue excitement, and no 
worrying and depressing anxiety. This is shown in the 
length of life that so often accompanies the quiet but 
laborious pursuits of science, while, on the other hand, the 
excitement and anxiety of a life of business, especially as 
it is ordinarily pursued in this country, are not favorable to 
longevity. 

373. Overworking the Brain. — It is especially 
important that the brain, during the period of its growth, 
should not be overworked. The reason is the same as 
that for the caution, so universally observed, in regard to 
putting too much labor upon the muscles of a young 
horse. And yet there is buoyant activity in the child, 
which is disposed to show itself in the operations of the 
brain as readily as in the action of the muscles. If this 
activity be turned into proper channels, and be not too 
much stimulated, no injury will be done to the delicate 
textures of the brain. 

Although much is said of the danger of over-stimulating 
the brain of the child, the difficulty does not so much lie 
here, as in the manner in which the mind is led to act. 
There is commonly too much of mere drudgery, and of 
storing the mind with unintelligible, and therefore unin- 
teresting matters. The mind, accordingly, is dissatisfied 
and wearied. The tedium of the labor exhausts, and so 
the brain is essentially impaired. When early education 
shall become in all respects what it ought to be, greater 
real acquisitions will be made without any injury to the 
growing brain. 

374. Influence of Quiet Cheerfulness. — It is 
well known that undue mental excitement and the depres- 



HYGIENE. 2G9 

sion of anxiety are together apt to produce insanity. 
Though they generally stop short of this result, they 
always injure the health aud shorten life. A firm and 
cheerful mind is favorable to longevity, but the anxious 
and fretting are seldom, if ever, long-lived. 

375. The Passions. — As the passions must have 
much influence upon the action of the mind, and therefore 
upon the state of the brain and nervous system, the proper 
regulation of them is essential to health and longevity. 
Much of the positive disease of the brain, and of the gen- 
eral nervous derangement so common among the educated 
and refined, comes from the bad management of the pas- 
sions. 

376* Alcoholic Stimulants. — There are certain 
articles in common use in the community, which produce 
so deleterious an influence upon the system, that they de- 
mand a more extended notice than can be given them in 
this chapter. Eeference is made to alcohol and tobacco. 
They act chiefly upon the brain and nervous system, 
the former as a stimulant, and the latter as a sedative. 
The use of opium is so limited compared with these, 
that it will not be dwelt upon, especially as it is never de- 
fended. 

Xo fact is more thoroughly demonstrated than that the 
system has no need of alcoholic stimulants while in a state 
of health. So far then as we look at mere necessity, these 
articles are to be considered simply as medicines, required 
only in diseased conditions. But it is said by some that 
they can be used in small quantities without injury to 
health. This cannot be claimed with any shadow of reason, 
except with relation to very small quantities. 

Entire abstinence is at least safe, and there are so many 
other things supplied by a bounteous Providence to gratify 
nd the appetite, that we can easily forego the 
of alcoholic stimulants; and we ought to be willing to 
do bo, if the good of others require it The common use 
of these articles as beverages is one of the most prolific of 
the g of disease ; and it is a significant fact, that the 



270 PHYSIOLOGY AND HYGIENE. 

very moderate use, claimed by some to be innocuous, has 
strong tendency to pass into a larger use, even so largi 
that its deleterious influence upon health is palpable. 

377. Tobacco an Active Poison. — The evidence is 
quite as clear in relation to the injurious effects of tobacco. 
This has sometimes been erroneously termed a stimulant. 
The error arises from the well-known discomfort of the 
habitual user of it when he is deprived of the use of this 
drug. This discomfort has a depressing influence, and 
when his system is brought again under the influence of 
tobacco the depression is removed, not by any direct stimu- 
lating effect, but by the relief given to the uncomfortable 
sensations. 

Tobacco is really one of the purest sedatives we have. I 
depresses vital action. It acts chiefly upon the nervous 
system, and therefore has a strong tendency to produce 
nervous diseases. While it is injurious to all, it is especially 
so to those who have a low vital action, and are disposed to 
nervous complaints. 

Tobacco is so active a poison that extreme caution is re- 
quired whenever it is administered, as it sometimes is, as a 
medicine. The effects of even a small amount of it upon 
one that is unaccustomed to its use are of the most de 
cisive character. And that must be an exceedingly artificial 
condition of the system, in which, by continued use of this 
drug, large amounts come to be borne with little apparent 
effect. 

The evidence of the deleterious influence of tobacco 
upon the system is as unequivocal as that in regard to the 
influence of opium, and wonderfully strong is that slavery 
to appetite that makes one persist in the use of this drug 
in spite of such evidence. 

378. Coffee and Tea. — Coffee and tea are often in- 
cluded in the same category with alcohol and tobacco. 
Granting all that is claimed in regard to the injurious 
effects of these articles, it is preposterous to class them 
with such poisons. The evidence in regard to them is con- 
flicting, and all that is settled as yet is, that in some persons 



HYGIEXE. 271 

they exert a bad influence upon the nervous system. 
It" this should be found to be true of a very large pro- 
portion of all who use them, the evidence would be con- 
clusive against the propriety of their use as common 
beverages. But as yet this has by no means been proved to 
be true. 

379* JPoisonous Emanations. — There are certain 
poisonous emanations, to which the human system is often 
subjected, that are largely destructive of health and life. 
They arise from decomposing filth of various kinds. Be- 
sides predisposing the system to the action of contagious 
and epidemic causes of disease, they also of themselves 
create disease. It is these emanations that render the close 
air of a crowded city, especially in its narrow lanes, so 
impure and fairly poisonous. And this impurity of the air 
is one of the chief causes of the difference in disease and 
mortality between the city and the country. The differ- 
ence is greater than is generally supposed. 

It has been found by statistics in England, that there are 
2-i per cent, more deaths from consumption, and 55 per 
cent, more deaths from typhus, in cities than in the rural 
districts, and the mortality from the diseases of childhood 
is twice as great in the city as in the country. In what 
way these emanations act we know not. But, although 
much is to be attributed to a mere want of ventilation, 
that is, to a lack of oxygen, there is no question that these 
emanations often act as positive poisons to the system. 

380. General J iew of the Causes of Disease. 
— In developing the principles of hygiene, we have noticed 
many of the prominent causes of ill health and disease. 
They are chiefly these: 1. A disregard in various ways of 
the rules relating to the digestive process. 2. Compression 
of the chest, especially during the period of growth. :). 
Deficiency in the supply of pure air to the lungs. 4. Fail- 
ure to guard properly against the influence of cold and heat, 
chiefly the former. 5. A lack of active exercise in the 
o air. 0. Overworking the muscles. 7. Errors in the 
management of the moral and intellectual powers. 8. The 



272 PHYSIOLOGY AND HYGIENE. 

influence of such articles as alcohol and tobacco. 9. Ema- 
nations from decomposing filth. 

It is well thus to look at these causes grouped together, 
endeavoring to give to each its due prominence. For vari- 
ous and exclusive views are often taken on this subject. 
Quite commonly some of these causes are kept entirely out 
of view, while others are strongly pressed upon our atten- 
tion. Disease is generally a very compound result, produced 
by a concurrence of several of these causes, and sometimes 
even of all of them. 

These causes of disease, it will be observed, are more or 
less under our control. Some of them are entirely so. A 
knowledge of their operation, and an earnest endeavor to 
remove them, would, therefore, vastly diminish the amount 
of ill health and disease. 

381. Our Control over the Causes of Disease. 
— It is true that there are some other causes of disease, of 
which we know but little, and over which we have little or 
no control. Such are the causes of various contagious and 
epidemic diseases. But these really produce a much less 
amount of disease than the causes which have been men- 
tioned. Their action is occasional, and confined to localities; 
not continual, and in all places. And besides, they may to 
a great extent be shorn of their power, by guarding against 
those causes of disease which are more or less under our 
control. It is those who neglect to do this that commonly 
become most readily the victims of contagions and epi- 
demics. 

382. Preventive and Curative Measures.— 
There is much interest in the community in regard to the 
cure of disease, but there is a blind indifference to its pre- 
vention. And yet vastly more can he done in the diminution 
of disease by preventive than ly curative measures. The 
ravages of consumption, for example, can undoubtedly be 
greatly lessened by preventing the operation of its principal 
causes; and yet what is said about these causes is little 
heeded, and the public attention is engrossed with the delu- 
sions of consumption-curers. 






HYGIENE. 273 

It is emphatically true of this malady, that multitudes 
more can be saved by preventive measures than by curative 
ones. Against no disease can hygiene achieve greater vic- 
tories. The neglect to use preventive measures against 
this and other diseases arises chiefly from the ignorance 
of the principles on which these measures are based. The 
prevalent indifference, therefore, to this subject can never 
be fully removed, till the general introduction of Physiology 
as a study into our schools shall make these principles 
familiar to the mass of the community. 



PART SECOND. 



CHAPTER XVII. 
CONNECTION OF THE MIND AND THE BODY. 



The Nervous System is to the mind the grand means of 
communication with the world of material and immaterial 
things around it. 

This communication is maintained through organs sub- 
ordinate to the nervous system. And you have seen that 
through the senses all knowledge of external things is com- 
municated to the mind, where it is used as the material of 
thought and feeling ; while, on the other hand, through 
the muscles the mind produces all its impressions upon 
external things. 

Let us now look more thoroughly into the connection 
which the nervous system establishes between the mind and 
the body, and observe some of the higher and more intricate 
phenomena which result from it. 

383. The Brain the Organ of the Mind.— The 
brain is the organ of the mind. In this life there can be no 
mental manifestations except through the agency of this 
organ. The mind and the brain always act together as one 
thing. This is manifest in regard to motion and sensation. 
It is equally true of thought. The mind can think and 
excite motion in the muscles only through the brain. The 
proofs of this are various and abundant. 

If a man by a blow upon his head have a portion of the 
skull driven in upon the brain, so as to press upon it con- 
siderably, all sensation and power of motion are suspended. 









CONNECTION OF THE MIND AND THE BODY. 275 

His mental connection with the world around him is com- 
pletely cut off. And furthermore, all mental action is ar- 
rested. The mind, thus shut in from the world around by 
the suspension of sensation, does not go on to act indepen- 
dently of the compressed brain. 

It may be remarked, that this degree of the suspension of 
the mental functions depends upon the degree of effect pro- 
duced upon the brain. If, for example, in the case of injury, 
the pressure of the bone driven in upon the brain be not 
very great, the suspension will be partial ; but if the pressure 
be considerable the suspension will be complete. 

384. Insanity a Disease of the Orf/anization. 
— Insanity is always the result of disease in the organization. 
This is so even when it is produced by moral causes acting 
directly upon the mind. The insanity in such a case is an 
indirect effect — the organization affected by the mind is 
thrown into a diseased state and reacts upon the mind, in- 
fluencing its manifestations. 

If the mind thus acted upon were a spirit, separated 
from the body, the result would be merely the feelings, 
which the motives applied would naturally produce, and not 
the unnatural feelings of insanity. It is not strictly proper, 
then, to speak of a "mind diseased." 

Let it nut be understood that mental derangement in every 
is to be attributed to disease that leaves such palpable 
traces that the dissecting knife would reveal it if death were 
to take place. There are diseased operations of the body 
that are hidden from our view — so hidden, that they not 
only kave no traces, but often develop no characteristic 
bodily symptoms. ■ 

383* Situation of the Brain. — Observe for a mo- 
ment the situation and the immediate connections of the 
brain, the organ of the mind. It is fitly placed at the sum- 
mit of the structure, inclosed by that noble dome which was 

ribed in the Chapter on the Bones. And then ob» 
that, in its immediate neighborhood, are the organs of four 
of the senses, sending their messages continually to the 
mind. Especially notice that under the jutting arches of 



276 PHYSIOLOGY AND HYGIENE. 

the front of the dome are the ever-moving eyes, looking out 
from their elevated place of observation ; and at the sides of 
the base of the dome are the halls of audience, ever open and 
ready to transmit the messages that come to the soul through 
the vibrations of the air. And there, too, in the very front 
of this habitation of the mind is the face, indicating by the 
delicate, quickly changing play of its muscles the thoughts 
that are at work within. And lastly, there is the mouth, 
the outlet for the voice, the chief agent of the outward man- 
ifestations of the mind. 

Here then are clustered together in this small space, in 
the immediate neighborhood of the mind's habitation, its 
principal instruments of communication with the world 
around. When we are listening to eloquence, whether it 
be in the public assembly, or in the social circle, or in the 
more private intercourse of friendship, and observe, as the 
rich tones proceed from the mouth, the elevated and change- 
ful expressions of the countenance, we are impressed with 
the idea that, if it be the mind which constitutes the 
image of God in man, the face of man thus situated in the 
front of the mind's habitation is the fitting outward emblem 
of that image. 

386. Rapidity of Communication between 
the Mind and Body. — It is interesting to observe how 
exceedingly rapid are the communications of the mind with 
the different parts of the body. Notice what the process is, 
or rather what the processes are, when you withdraw your 
hand from any thing that hurts it, as heat for example. An 
impression is produced upon the expanded nerve in the 
part — this impression is sent along the nervous tubuli to the 
brain — the mind there receives the impression — the mind in 
return communicates an impression to the brain — this im- 
pression goes by another set of nervous tubuli to the mus- 
cles — they act, and the hand is withdrawn. If it took as 
long to do all this as it has to describe it, the hand would be 
very thoroughly burned before it is drawn away. 

387. Skill in the Use of the Muscles. — The use 
which the mind makes of all the machinery of the senses 






CONXECTIOX OF THE MIND AND THE BODY. 277 

and of the organs of locomotion does not come to it at the 
outset. It comes by training, and in some cases by very 
long training. The child at first uses its muscles bunglinglv. 
It does not see or hear skillfully. It knows nothing at first 
of the colors, or shapes, or distances of objects. It knows 
nothing of the direction or distance of sounds. It has all 
these things to learn. And for this purpose the organs of 
sense and the muscles are put into exercise at once, and 
the child begins its long process of learning on the day of its 
birth. 

Few have any conception of the amount of knowledge 
which is acquired in the first of the child's life. Not only 
is he born with absolutely no knowledge of the world of 
things around him, but he has no skill in the use of the 
instruments, the muscles and the senses, by which he is to 
obtain his knowledge. These give him at first no very defi- 
nite information : but by the constant exercise of them, 
and by comparisons between the reports of the different 
senses, he soon adds rapidly to his stock of knowledge, and 
becomes skillful in the use of his means of gathering it. 

388. Skill in the Use of the Senses and the 
jrusclcs. — Skill in the use of the muscles varies much in 
different individuals. It is wonderful in the juggler, the rope 
dancer, the skillful player on a musical instrument, and the 
accomplished singer. You will have some conception of 
what education can do for the muscles, if you contrast the 
awkward balancing of the child in walking with the agile and 
delicate balancings of the rope-dancer, or the aimless and 
uncouth movements of the infant's hands with the rapid and 
varied execution of the player on an instrument, or the monot- 
onous and coarse Bounds attered in a child's first attempts 
at singing with the varied melody of a skillful singer. 

The senses are educated as well as the muscles. As you 
an infant reaching out his little hands awkwardly 
with his unskilled muscles towards an object, it is manifest 
that he knows not at what distance the object is from him, 
and that lie does nol readily adjust his eyes to its distance, 
so as to cee it clearly. 



278 PHYSIOLOGY AND HYGIENE. 

He after a while by practice acquires the power of doing 
this. The same may be said of hearing. The little muscles 
described to you as so nicely adjusting the eye for seeing at 
different distances, and the ear for hearing various notes of 
sound, require training, just as the muscles do with which 
we walk or talk. 

389. The Senses and the Muscles Mutual 
Teachers.— The senses and the muscles are mutual teach- 
ers in the education here described. Thus, in singing, the 
accuracy of the sense of hearing in estimating sounds is 
acquired through the action of the muscles of the voice 
while the ear is listening. And on the other hand, skill in 
executing sounds is acquired by these muscles under the 
tuition of the ear. The dependence of the senses upon the 
muscles is not absolute, however, as is that of the muscles 
upon the senses. 

The ear can be trained in the accurate appreciation of 
sounds without any corresponding exercise of the muscles 
of the voice, though the two processes are ordinarily to 
a greater or less extent connected, and are corrective of 
each other. But even when the ear is trained without any 
aid from the muscles of the voice, the training is in some 
measure a training of muscles. 

For there are certain little muscles that regulate the ten- 
sion of the drum of the ear, which undoubtedly go through 
a process of training when we are learning to distinguish 
accurately between different notes of sound. While the de- 
pendence of the senses upon the muscles is thus a partial 
one, the dependence of the muscles upon the senses is, on 
the other hand, complete. 

Although the muscles have a sense of their own, a mus- 
cular sense, as Bell calls it, this is not adequate to be their 
sole guide in action, but it serves as a mere auxiliary in this 
respect. This absolute dependence of the muscles upon the 
senses is very strikingly shown in the fact, that the deaf and 
dumb are dumb simply because they are deaf. The voice 
in them has no teacher. 

390. The Involuntary Muscles not JEdu- 



CONNECTION OF THE MIXD AXD THE BODY. 279 

cated. — The education of the muscles does not extend to 
those which are involuntary. Though respiration, for ex- 
ample, is a very complicated act of many muscles, these 
muscles require no education to do their part skillfully. 
We have no need to superintend them, for their constant 
action is secured by an arrangement for nervous influence 
which is independent of the mind. 

S '. while the mind sleeps, or when it is locked up in the 
stupor of disease, these muscles continue to perform their 
duty, as well as when we are awake. The same substantially 
can be said of the muscles which perform the act of swallow- 
ing. Although this is a very compound, and, mechanically 
considered, a very difficult act, it is performed as well in the 
first hour of the child's life as it is at any future period. 
The muscles that execute ife need no training. And yet it 
is only after long and diligent training that the purely vol- 
untary muscles, as for example those of the hand, execute 
movements which are no more complicated and difficult. 

The reason for this difference is obvious. The movements 
which are performed by the involuntary muscles, such as 
breathing and swallowing, are immediately essential to the 
preservation of life, and it is therefore necessary that they 
should be well executed from the first. The voluntary mus- 
cles, on the other hand, instead of being devoted, like the 
involuntary, to the maintenance of life, act as the instru- 
ments of the mind, and therefore the mind acquires the 
power of using them skillfully only by dint of long-continued 
training. 

391. Association of Adtion in the ^Muscles 
without Mental Action* — In the education of the 
muscles, it is to be observed, that although the mind, during 
the process of learning, at first takes distinct cognizance of 
every movement, it after a while, as the education becomes 
complete, takes little or no notice of many of the move- 
ments, pt when some error occurs, or some obstacle 
hen one' is learning to ring or play a tune, 
mind, through the car, at first takes a d< finite and dis- 
tinct notice of every Bound, and makes an appreciable exer- 



280 PHYSIOLOGY AND HYGIENE. 

tion in every movement. But after the tune is learned, this 
ceases to be the case, and the movements seem to be asso- 
ciated together, in some measure independently of mental 
action. 

So in learning to walk, the child notices each of his move- 
ments very distinctly. When, however, he has fully learned, 
but little thought seems to be expended upon the motions, 
except when some obstacle appears which interrupts their 
regular succession. When one walks in a reverie, the mind 
is most of the time wholly abstracted from the associated 
movements which make up the compound act of walking. 

In learning to read, the child makes a distinct mental 
effort in regard to each letter, resorting to every aid which 
will help to make the effort a successful one, even to 
putting the finger on each letter as he looks along the line. 
But as he becomes more and more skilled, the association 
of action comes more and more into play. 

392. Offices of the Cerebrum, and Cerebel- 
lum. — In the Chapter on the Nervous System, the different 
offices of the different central organs of this system were 
mentioned. The brain, as you have seen, is more especially 
connected with the mind, and is the great instrument 
through which mental manifestations are made. But it is 
only a certain part of the brain, the cerebrum, a, Fig. 110, 
that has this special connection with the mind. The cere- 
helium, h, Fig. 110, it is supposed, is especially devoted to 
the motions of the body, for in different animals it is de- 
veloped in proportion to the # range and variety of motion. 

From extended observations on this point in comparative 
anatomy there seems to be good reason to conclude, that the 
cerebellum is the great central apparatus for combining the 
various compound motions of the body. It is uniformly 
found to be larger in those animals that have great compli- 
cation in their muscular movements, than in those in which 
these movements are of a simple character. 

Thus, in animals whose most complicated motion is walk- 
ing, as the hoofed quadrupeds, the cerebellum is much smaller 
than in those animals that climb and take hold of things 



CONNECTION OF TIIE MIND AND THE BODY. 281 

with their paws. In man it is much larger than in any 
other animal, for he walks erect, and thus brings into action 
a very large number of muscles in this delicate balancing 
movement (for such it is), and then, in the individual parts 
of the body, especially the hand, he executes a great range 
of very complicated movements. It is more developed in 
monkeys and apes than in any other of the inferior animals, 
because, with their capability of extensive variety of posture, 
and their power of seizing objects with their extremities, 
they obviously come nearer to man than any other animal 
in the varied combination of their muscular action. 

The conclusions thus arrived at by comparative observa- 
tions in animals have been continued by experiments. It 
has been found by physiologists, that if the cerebellum be 
removed with as little disturbance as possible to other parts, 
although the sensibilities remain, and motions are performed, 
the power of combining muscular actions in definite com- 
pound movements, such as flying, walking, &c, is lost. 

In relation to the cerebrum, we rind that the amount of 
intelligence depends on the amount of its gray portion, the 
vesicular substance. In man, therefore, this part of the 
cerebrum is very much greater than it is in any other animal. 
It is the difference in the amount of the gray substance 
which constitutes the grand distinction between the brain 
of man and that of any of the higher orders of animals, for 
in all other respects his brain seems to differ little from 
theirs. 

In looking at representations of the brain, as in Fig. 112, 

it would seem at first view that the gray substance, the 

working part of the cerebrum, is much less in amount than 

white portion, which serves only tor transmission. But 

this is not so. The eye is deceived, because the white >ub- 

gether in <>ne central mass, while the gray 

• is spread oul in an external layer. This is rery 

plainly illustrated by Fig. 158. Here the area, ". contained 

in the inner circle, strikes the eye as being larger than the 

;. h. included between the two circles, and yet these areas 

are ; - equal. 



282 



PHYSIOLOGY AtfD HYGIEXE. 



Observe for a moment, in this connection, the concurrent 
evidence by which we determine what the function of the 
gray substance of the brain is. It comes from two sources. 
The first is that which is furnished to us by the structure of 
the cerebrum. As heretofore stated, the gray portion is 
made up of cells, while the white portion is composed of 
tubuli. These tubuli are such as we find in the nerves, and 

Fig. 158. 




in fact are continuous with them. We very properly infer, 
therefore, that as the nerves serve only for transmission, the 
white part of the brain does the same. It has, therefore, 
nothing to do with the thinking, and yet we know from 
other facts that this is done in some part of the cerebrum. 
So we necessarily infer that it must be done in the gray 
substance. And here, to confirm the truth of this inference, 
comes in one other source of evidence, viz., the comparison 
between different animals in regard to the correspondence 
between the amount of the gray substance and the amount 
of intelligence. 

393. Facial Angle. — The size of the anterior portion 
of the brain, above referred to, may be estimated by the 



CONNECTION OF THE MIND AND THE BODY. 



283 



measurement of the facial angle. This angle is formed by 
drawing two lines as represented in Figures 159 and 160. 
The line, a, b. is drawn from the most prominent part of the 
forehead to the front of the upper jaw. The line, c, d, is 



Fig. 159. 





intended to represent the line of the base of the brain, and 
runs from the orifice of the ear along on the floor of the 
cavity of the nose. It is manifest that the less prominent is 
the forehead, that is. the less brain there is in the front part 
of the head, the more acute will the angle be that is formed 
bv these lines. In Fig. 160, which represents the skull of a 
negro, this angle is more acute than in the skull of the 
Europeau, Fig. 159. In animals this facial angle is much 
more acute than in man. In the monkey tribe it varies 
from G5 C to 30°, while in man its average is about 75°. The 
ancient Greeks, wishing to give the aspect of great intellec- 
tual superiority to their statues of deities and heroes, made 
it in them as high as 90°. 

It is proper to remark here, that while it is clear that, as 
ueral rule, the amount of intelligence is to some extent 
proportioned to the amount of the cerebrum, both in man 
and in animals, the rule is not an invariable one. Size is 
far from being the only measure of power in this case. 
What differences there may be in intimate structure, to com - 
pare with the mental differences, we know pot Even where 
the nil.* stated above hold.- good, tin,' difference in mere hulk 
i- far from being proportionate t<> the mental difference. 
mind of a Newton or a Shakspeare is gigantic compared 
with any common mind, but the brain in such cases is not 
very much larger than ordinary brains. 



284 PHYSIOLOGY AKD HYGIENE. 

394. Mental Difference between Man and 
other Animals. — In relation to the evidence drawn from 
a comparison between different animals in regard to the 
functions of the nervous system, there is one significant fact 
which must not pass unnoticed. Though, as we rise in the 
scale of animal life in our observations, we find every new 
addition of functions coupled with some new additions of 
structure until we come to the higher animals, we do not 
find this to be so when we pass from them to man. 

The brain, it is true, is larger in man than it is in them, 
and has much more of the gray substance ; but there are no 
essential differences of structure in his brain, to correspond 
with the added mental qualities which so decidedly distin- 
guish him from the brutes. These qualities constitute some- 
thing more than a difference of degree. It is a difference of 
hind. And, therefore, it is a great and a significant fact, that 
there is no corresponding difference of kind in the organiza- 
tion of the brain. 

The distinction between man and other animals is a defi- 
Aite one. It is as definite as it would be if it were based 
upon difference of organization. The barrier is fixed ; and 
not a step over it has any animal advanced, with all the 
training which may have been expended upon him. No 
animal, however intimate his intercourse with man, has ever 
acquired man's habit of abstract reasoning, or manifested 
any real knowledge of the difference between right and 
wrong. Prof. Guyot does not speak too strongly when he 
says, "I will even go farther than is ordinarily done, and I 
will say, that there is an impassable chasm between the 
mineral and the plant, between the plant and the animal; 
an impassable chasm betiveen the mere animal and man." 

395. Sources of Evidence in regard to the 
Nature of the Connection betiveen Mind and 
Body. — The nature of the connection of the mind and the 
body is a great mystery. Still, there are many things which 
we can know in relation to it. The sources of our knowl- 
edge on this subject are three, viz., the investigations of 
Physiology, the testimony of Consciousness, and that of 



CONNECTION" OF THE MIND AND THE BODY. 285 

Revelation. Each of these kinds of evidence throws light 
upon the others. If, therefore, we nse all of them, giving to 
each its due limits and force, we shall come to some certain 
and valuable conclusions. But if we take any one of them 
alone, we shall be liable to be led into gross error. 

In the investigation of this subject, there is in some physi- 
ologists a disposition to rely upon physiology alone, to the 
exclusion of the other sources of evidence. In doing this 
they are driven to this alternative: either they must be 
content with a very limited knowledge of the subject, or they 
must rely upon mere presumptive evidence for many of their 
conclusions. And commonly the latter is the course which 
they pursue. They are not content with the very limited 
conclusions to which they are shut up by the absolute proof 
furnished by physiology. 

They boldly reason, therefore, upon what they deem to be 
probable. And they are invariably led into error. 

XiHi. Endowment* of 3Iatter. — In order to get 
definite ideas of the manner in which the erroneous conclu- 
sions are arrived at, let us view matter in its various states 
and connections. Unorganized dead matter, in some im- 
portant respects, is entirely different from living organized 
matter. The distinction is a definite one. It is easily recog- 
nized, and none but dreamers in science have failed to see it. 

Living matter is endowed with certain properties that 
dead matter has not. They are termed vital properties. 
They control to a certain extent the mechanical and chemical 
properties which both forms of matter have in common. 
Borne suppose that what we call life is a single principle; 
but others suppose the endowment to be compound, made 
up of different principles or properties. But this question 
we need not discuss. All that concerns the view here pre- 
ted is the mere foci of the endowment. 

Lei us go ;i step farther. Some living beings have more 
endowments than others. All have those of organic life in 
common. But there is an animal life also, which by means 
of the nerv( peradded to the organic And, 

as we trace the animal kingdom from tfa • lowest animal up 



286 PHYSIOLOGY AND HYGIENE. 

to man, we find the endowments connected with this system 
multiplied as we advance, till in him they are more compli- 
cated and extensive than in any other animal. 

This is especially true of intellectual endowments, those 
which are merely instinctive being more developed in many, 
perhaps we may say most, of the inferior animals. And in 
man we find special mental endowments, of which other 
animals present not the faintest trace. 

397. Is Intelligence One of them ? — Now the 
question arises, whether intelligence is like life, a mere en- 
dowment of matter, or whether it is in some measure inde- 
pendent of it. In other words, whether it is a principle or 
set of principles with which matter is endowed, or an imma- 
terial something which acts through matter as its instru- 
ment. How much does bare physiology teach us on this 
question ? It has often been claimed that it can teach us 
much, and the most bold conclusions have sometimes been 
ventured from this quarter. But mere speculation has in 
all such cases been deemed to be proof. Physiology does 
show us, as before stated, that the spiritual is in this world 
always connected with the material, and that mind never 
acts independently of the matter with which it is connected 
in the brain. But it gives us no light upon the nature of 
this connection. It is well for us to know how deficient are 
its teachings on this point. 

For all that it can teach us, we know not but that the 
mind may be a mere result of action in matter. It neither 
tells us that it is so, or that it is not. It leaves us entirely 
in the dark on this point. Indeed so far as it affords pre- 
sumptive evidence, it appears to teach, that mental phe- 
nomena are results of matter, acting in consequence of cer- 
tain endowments or tendencies imparted to it, just as secre- 
tion is in living substances, or chemical action in those 
which are not living. 

Accordingly those who have relied upon physiology alone 
on this subject, have adopted various forms of materialism. 
Some have supposed that thought is a mere product of 
matter, and that the brain secretes it as the liver secretes 



CONNECTION OF THE MIND AND THE BODY. *2ST 

bile. Others have taught that the mind is "a bundle of 
instincts." each residing in some particular part of the brain 
as its organ. This has been the doctrine of some prominent 
phrenologists. 

Let us look at living matter in another point of view, and 
see to what physiology alone, if at all venturesome in draw- 
ing conclusions, will lead us. Let us look at the origin and 
growth of the thinking animal. Take, for example, an ani- 
mal the formation of which we traced in the Chapter on 
Cell-Life. The beginning of the bird as it forms in the egg 
is a simple cell filled with a fluid. This produces other 
cells, and soon the organs and the limbs of the animal are 
formed. At length the animal bursts the shell, and comes 
out not only a living and sentient being, but a thinking 
being. It has a mind which feels desires and emotions, and 
prompts the muscles to action to effect its purposes. 

Organization here precedes the development of mind so 
far as we can see, and therefore it would seem that mind is 
a result of organization. Especially does this appear to be 
so. when we find that the amount of mind in different ani- 
mals is proportioned to the amount of a certain part of the 
organization, the brain. All this is as true of man as it is 
of other animals. And besides, w r e see in man that as the 
organization becomes perfected, the intelligence is propor- 
tionally increased. 

In infancy, when the organization of the brain is imper- 

f vt, the intelligence is small in amount, and grows with the 

• th, and strengthens with the strength of the brain. 

And as the mind thus grows with the body, it appears to 

Mi with the dissolution of the organization, and in the 

3e of the inferior animals undoubtedly does so. 

But the evidence from physiology does not all tend to 
materialism, 'filer.- is some negative evidence which has a 
diff aring, in tli«' fad that, while man differs in his 

itual nature so widely and so specifically from the infe- 
rior animals, his brain exhibits no corresponding specific 
difference in structure but only a difference in amount. 
The difference in d of intelligence in the animals 



288 PHYSIOLOGY AND HYGIENE. 

below man is marked by a corresponding difference in the 
amounts of the gray substance. 

And if it were true that man, as some think, differed from 
them only in having a higher degree of intelligence, we 
should expect to find in him a mere increase of this sub- 
stance. But as his mind differs from theirs not merely in 
degree, but in kind also, we should have reason to expect, 
if mind were wholly dependent on organization, that the 
anatomist would find not only an increase in the quantity 
of the gray substance, but also a difference in its structure. 

398. Physiologist needs other Evidence. — It 
is quite clear then, that the physiologist cannot well avoid 
materialism, if, in examining the connection between the 
mind and the body, he rejects all evidence beside that which 
physiology furnishes. He can be saved from this result only 
by being content with the narrow limits to which he is 
shut up, if he confine himself to absolute proof. As we 
have already seen, the positive knowledge that physiology 
gives us on this subject is exceedingly narrow. We soon 
come to the line that divides the known and the supposed. 
And if we attempt to go beyond that, our conclusions as 
to what is probable will quite certainly lead us to the result 
pointed out. 

The need, therefore, of the evidence drawn from the other 
sources mentioned is most palpable. The physiologist must 
confess himself to be under the necessity of going out of his 
physiology, in order to learn all that can be learned upon 
this subject. At the best, there is much mystery in relation 
to it which we cannot penetrate, with all the light that we 
can bring to bear upon it. And the mystery is deep indeed, 
when we call to our aid only the dim light of physiology. 
It needs some other light to deliver us from the confusion 
of ideas, into which we are introduced by the analogy exist- 
ing between the phenomena of life and instinct and intelli- 
gence, in relation to their connection with the organization 
of matter. Let us look then at the evidence which comes 
from the other two sources, viz., our consciousness, and reve- 
lation. 






CONNECTION OF THE MIXD AXI) THE BODY. 289 

399. Consciousness. — Every individual is con- 
scious that, as he feels and thinks and acts, he, that is, his 
mind or spirit, acts upon the structure of his body, and is 
acted upon by it. It is not a consciousness that he, as a 
material body, does all this, lie feels that it is a power 
within that does it, and he instinctively separates in his 
ideas the power from the different parts of the body, and 
from the body as a whole. He is conscious, too, of a responsi- 
bility in relation to the thoughts and acts of the spirit 
Within. He has a knowledge of right and wrong, and lias 
self-reproach on doing wrong, and self-approbation on doing 
right. 

It is this consciousness of a self-acting immaterial spirit in 
this material body, that constitutes the basis of all character, 
and of all the moral relations of man to his fellow-man, 
and to his Maker. Everybody acts upon the testimony of 
this consciousness as being valid and certain testimony. 
And, however the physiologist may reason about matter 
and mind, as if the latter were a mere product or endow- 
ment of the former, yet as a man, as a member of society, 
as a subject of government and law, he cannot avoid acting 
upon the ground that mind in a certain sense controls 
matter, and is responsible for its acts independently of the 
matter with which it is connected. 

400. Evidence front Consciousness Con- 
firmed by Revelation. — Now the evidence which this 

lord- us should suffice to keep us from the 
materialism into which physiology taken alone would be 
apt to lead us. It shows us that, although the mind is de- 
veloped witli the material organization, and can act only 
with it, it is not its mere product, nor one of its endow- 
ments. It shows us, on the other hand, that it is in some 
measure independent of matter, and that its dependence 
upon it is only a dependence of connection, matter being 
the instrnm -nt of mind, through which it acts on external 
things, and is acted upon by them. The evidence from this 
son re- is of a positive character. 

We are driven by it to the alternative of believing that 
13 



290 PHYSIOLOGY AND HYGIENE. 

the mind is an immaterial, self-acting agent, in some meas- 
ure independent of matter, or of harboring the impious and 
monstrous belief that the Creator has implanted in the 
bosom of man a lie, and that he is living a horrible farce, 
acting in view of moral relations and responsibilities that 
have no existence. 

This positive testimony of our consciousness is confirmed 
by the testimony of revelation. This is not done by any 
formal array of proof. The existence of the spiritual part 
of man as a self-acting responsible agent is assumed as a 
fact that needs no proof. All the statements, and teachings, 
and appeals of the Bible recognize it as a fact known to the 
consciousness of every man. The Bible, therefore, may be 
considered as simply affirming that the testimony of our 
consciousness on this point is valid testimony. 

But the Bible goes farther than this. It gives us one 
great fact of which neither physiology nor our consciousness 
could assure us, namely, the mind's immortality. Our con- 
sciousness could, it is true, give us presumptive evidence to 
show that the soul with its high powers and aspirations is 
to live after the death of the body. But it could furnish us 
no absolute proof of the fact. And its presumptive evi- 
dence would be effectually rebutted by the presumptive 
evidence from physiology, which, as you have seen, points 
in another direction. 

We are so familiar with the mind's immortality as a 
known fact, and we so uniformly think of it in connection 
with the death of the body, that we are not aware how abso- 
lutely dependent we are upon revelation for all that we 
know in relation to it. If there were no revelation, and 
death were to us an unknown event, and we were now for 
the first time called upon to witness the death of a friend, 
how little should we know, and how confused would be our 
thoughts in relation to the great mystery before us ! " What 
is it?" we should ask. "Is it sleep ? No. We never saw 
any one sleep thus. What is it ? Who can tell us ? " And 
we should wonderingly watch to see some signs of awaken- 
ing, not giving up all hope till decay begins its ravages on 



CONNECTION OF THE MIND AXD THE BODY. 291 

the loved form before us. Then, as we should from the dic- 
tate of nature, consign to the earth the friend who was so 
recently among- us a breathing, moving, speaking man, now 
a mere mass of decaying matter, we should feel that we bury 
there not the body only, but all that belonged to that body 
during life — the whole man. 

Thought and feeling, as well as life and motion, would 
appear to us, untaught of God, to be extinguished in the 
grave. Even if some one should utter all tremblingly the 
hope that there might be a subtle, spiritual part of our 
friend that would some time, in some form, return again to 
our society, that hope would at once be crushed by the re- 
flection that whatever it was in our friend that thought and 
felt, it came into existence with the body, was infantile when 
the body was, grew with the growth of the body, and 
strengthened witli its strength, and therefore now, so far as 
we can see, has perished with it. Nature utters no voice 
to tell us otherwise. She emits no light to illuminate the 
grave. Darkness and silence rest there, till the light of reve- 
lation shines upon it. and God proclaims man's immortality. 

Your attention has been called to the three sources of 
evidence in regard to the connection of the mind and the 
body, and the character of the evidence furnished by each 
has been indicated. It has been shown particularly that if 
the attention be confined to that which is furnished by 
physiology, the mind is apt to be led into materialism. But 
the attention should not thus be confined. All the three 
kinds of evidence should he employed and should be brought 
to bear upon each other. 

If this be done, the discrepancies in the evidence from 
physiology are cleared up by the evidence afforded by con- 
iation. and we see the true value and 
ring of the fact, thai the specific mental difference between 
man and animals is n«»t attended with a corresponding 
structural diffi rence. Though this fact operates merely as 
conflicting evidence, when taken -imply in connection with 
the rest of tie- facte developed by physiology; when we 
come, on the other hand, to take the whole range of evidi 



292 PHYSIOLOGY A^B HYGIENE. 

from the three sources spoken of, it is exceedingly satisfac- 
tory as concurring with the testimony of consciousness and 
revelation. 

At the same time, those physiological phenomena, which 
taken by themselves seem to show so strongly that the mind 
is wholly dependent upon organization, are so interpreted 
by the evidence from the other sources, that the dependence 
is seen to be for the most part a dependence of connection 
only, the brain being the instrument of the mind. 

The evidence from consciousness and revelation is of the 
most positive character, and can not be set aside by evidence 
from any other source. Other evidence may serve to inter- 
pret it, but can not nullify it. The attempt is sometimes 
made to set it aside by urging the presumptive evidence of 
physiology, as if it were absolute proof. But most physiolo- 
gists engage in no such futile and unchristian efforts, but 
give due weight to the testimony of consciousness and reve- 
lation in all their investigations of the mysterious connection 
of the mind and the body. 

The influence of Carpenter, an English physiologist, 
whose works are more extensively used by students than 
those of any other physiologist, is especially to be commended 
in this respect. And although skepticism occasionally 
utters its plausible falsities, deceiving the superficial and the 
speculative, we have no fears from present indications that 
the votaries of physiological science will, as a body, be ar- 
rayed in opposition to Christianity. 



CHAPTER XVIII. 

DIFFERENCES BETWEEN MAN AND THE INFERIOR 

ANIMALS. 

The differences between man and the inferior animals have 
been alluded to in different parts of this book, and especially 



MAX AND THE INFERIOR AXIMALS. 293 

in the preceding chapter. But it has been done only inci- 
dentally, and the subject demands at our hands a more 
thorough and systematic investigation. 

401. Views of Lord Man boildo.— Lord Monboddo 
maintained that man is only an improvement on the monkey, 
occurring as a result from the general tendency to advance- 
ment claimed to exist in nature. He seemed to think that 
man bore a relation to the monkey somewhat like that which 
the frog bears to the tadpole, and that as the tadpole becomes 
the frog, so the race of man was produced by a change, at 
some remote period of the creation, of the monkey into the 
man. 

This ridiculous notion of the erudite but fanciful Scotch 
philosopher is really but another phase of the more recent 
theory of gradation, or development, as it is sometimes 
called, which in different forms is now advocated by so many 
European philosophers. And, although few, comparatively, 
adopt this theory definitely and fully, there is quite a dispo- 
sition among many to obliterate the distinctions by which 
the Creator has in so marked a manner separated man from 
the inferior animals. It is well, therefore, that we should 
have a clear idea of these distinctions. 

It is often very loosely said that while man is governed 
by reason, instinct rules in the animal.* If it be meant by 
this that, as a general rule, reason predominates in man, 
while instinct does so in animals, the statement is a correct 
one. But if it be meant that animals are wholly governed 
by instinct, and that man is distinguished from them as a 
\ tning animal, it is not correct For some animals do 
I m, that is, if making inferenc l msidered as rea- 

son: 

* Some explanation may be well here in relation to the different uses 
made of the word animal in different 0ODH< Bere it Ifl need in 

jtinctioo to man. So it is used in the expression, man and 
animals But as man is in certain senses an animal, whenever we wish 
to recognize this fart we speak of other animals is ti animals. 

And thus, in regard to an'in. peak of their higher and lower 

orders, the higher of course being (hose that approximate nearest to 

man. 



294 HYSI0L0GY AND HYGIENE. 

In tracing out the difference between man and animals no 
attempt will be made to show what the nature of instinct is. 
This is a great mystery, and all attempts to solve it have 
utterly failed. Let us examine some of the differences 
between instinct and reason. In doing this it is not always 
easy to say just where the one begins and the other ends, so 
intimately are their phenomena often mingled together. 

The actions of instinct are more unaccountable than 
those of reason. In the operations of reason we see some- 
thing of the processes by which results are reached. For 
example, as a man travels oyer an unexplored country, we 
can understand by what means he obtains a knowledge of 
the country, in order to guide him on his journey. The 
processes of his reasoning in regard to this we can compre- 
hend. 

But when an insect travels with unerring certainty to its 
place of destination without any guide-marks that we can 
see, or when a swarm of bees or a flock of birds wing their 
flight to distant places, or when bees construct their honey- 
comb with the exactness of mathematics in obedience to the 
best principles for such a structure, we can not understand 
the processes which lead to the result. It seems to be pro- 
duced by an impulse from a cause extraneous to the ani- 
mal, guiding it as if it were a mere machine. The little intel- 
ligence of the animal seems to have only an incidental con- 
nection with this impulse. It, therefore, merely controls 
somewhat the circumstances under which the instinct acts. 

402. Instinct Governed by Invariable Hides. 
— So little has the intelligence to do with the instinct, and 
so nearly mechanical therefore are the actions of the latter, 
that they are governed by an invariable rule. It is nearly 
as invariable as are the movements of a machine. For this 
reason there are no improvements or alterations in the acts 
of instinct. 

The bird and the bee, for instance, have no change of 
fashion in their architecture from age to age. The honey that 
fed John the Baptist, or that which was found by Samson 
in the carcass of the lion, was deposited in the same hexag- 



MAX AXI) THE INFERIOR AXIMALS. 



295 



onal cells which are constructed by the bees of the present 
day. 
403. Contrivances in the Nests of Birds. — 

Each bird builds its nest precisely in the same way that 
its ancestral birds have ever done. Most birds' nests are 
constructed after the same general pattern. But sometimes 
we observe striking peculiarities to subserve some special 
purpose. 

Fig. 161 represents the nest of the Baya, a little bird of 
Hindoostan. It is in the shape of a bottle, and is made of 

Fig. 161. 




NEST OF THE BAYA. 



long grass. It is suspended from a slender branch of a 
. so that monkeys, serpents, &c, cannot reach it. The 
entrance to the nest is made on the under side, so that these 
animals cannot enter, while the bird itself can readily fly in. 
It is divided into apartments, in one of which the female 
sits upon the eggs, while in the other the male bird "solaces 
his companion with his Bong whilst she is occupied in ma- 
ternal car-." In Pig. L62 is Been the nesl of another little 
■rn bird, which with filaments of cotton taken from the 
cotton plant, a >ws leaves together with its beak and feet, so 
as to conceal the inclosed nesl from its enemies. 
404. Contrivances in the Honey-comb. — 



296 



PHYSIOLOGY AOT HYGIENE. 



Fig. 162. 



While there is no change in the acts of instinct they are 
marked by perfection. There is nothing in which this per- 
fection of instinct is better shown than in 
the construction of the honeycomb. The 
cells are made hexagonal, because in this 
way all the space is occupied— there is 
no waste of room. If the cells were 
made circular, there would not only be a 
waste of room, but a large quantity of 
material would be needed to fill up the 
spaces between the cells. The diiference 
can be seen in the two Figures 163 and 
164. Each comb, it is to be observed 
farther, has two sets of cells, the ends of 
one set being arranged against the ends 
of the other in a peculiar manner. These 
ends are not flat, but each one has three 
plane surfaces, forming with each other 
a particular angle soon to be noticed, 
and uniting together at the center in a 
point. In the arrangement of these cells, 
therefore, a cell of one set does not lie 
end to end with a cell of another set. 
Its three surfaces form a part of the bot- 
tom or end of three cells of the other set. This is made 




NEST 
of the Tailor Bird. 



Fig. 163. 



Fig. 164. 





clear by Fig. 165, in which a cell of one set is repre- 
sented as it abuts against a cell of the other set by one of 



MAX AXD THE INFERIOR AXIMALS. 297 

its surfaces, its other two surfaces forming a third part of 
the ends of two other cells. 

Now it has been found that the Fig. 165. 

angle formed at the edge of these . -^ 

surfaces between the two sets of cells ^ 

- ich as to secure the greatest V— - -^ \ : ~"~M» 
strength with the least amount of 
material. It was at one time 

thought that this was proved to be not exactly true. The 
variation from the correct angle, made out by the calcu- 
lations of the mathematicians, was indeed a slight one, but 
still it was variation enough to show, if the calculations were 
correct, that the workings of instinct were not perfect in 
this case. But the investigations of Lord Brougham have 
satisfactorily shown that the mathematicians were wrong in 
their calculations, and that the bees are right. 

40<~>. Wonderful Operations of Instinct in 
Communities anion*/ Animals. — The perfection 
of the operations of instinct is shown in the most wonder- 
ful manner in the regulation of cnmimniitics of animals. 
Here we see cooperation to produce results effected through 
an irrational, and therefore in some measure a blind instinct. 
This social instinct is most extensively exemplified among 
the insect tribes, as for instance the bee and the wasp. The 
structures resulting from the cooperation of multitudes 
of little laborers guided by this instinct, arc very interest- 
ing. Take but a single familiar example, the construction 
of the nests of wasps. These insects make their building 
material from the fibres of old wood. These they convert 
by mastication into a pulp, which made into a thin layer, 

somes firm like paper. It is indeed a process very much 
like the common process of paper-making invented by man. 
and the first rude inventor may have got his idea from the 
•t. With this substance the wasps build several nu 

3, which are hexagonal, like the cells in the comb of 
bee. These ranges of cells are placed parallel t<> each 
other, at regular distances, with little supporting columns 
between them, as seen in Fig. 1GG. 



298 



PHYSIOLOGY AND HYGIENE. 



The number and variety of instincts of the ordinary hive 
bees are very wonderful, but it would occupy too much 
space to describe them. 



Fig. 166. 




NEST OF WASPS. 



406. JEocemjilified in the Beaver Commu- 
nity. — The wonderful cooperation of animals in obedience 
to social instinct, in the building of habitations and other 
structures, is seen in several of the mammalia. But it is 
most wonderful in the beaver, the following description of 
whose habits in this respect is taken from Carpenter: 

u During the summer it lives solitarily in burrows, which it 
excavates for itself on the borders of lakes and streams ; but 
as the cold season approaches it quits its retreat and unites 
itself with its fellows, to construct, in common with them, 



MAX AXD THE INFERIOR ANIMALS, 290 

a winter residence. It is only in the most solitary places 
that their architectural instinct fully develops itself. Hav- 
ing associated in troops of from two to three hundred each, 
they choose a lake or river, which is deep enough to prevent 
its being frozen to the bottom; and they generally prefer 
running streams, for the sake of the convenience which 
these afford in the transportation of the materials of their 
erection. 

'• In order that the water may be kept up to a uniform 
height, they begin by constructing a sloping dam; which 
they form of branches interlaced one with another, the 
intervals between them being filled up with stones and mud, 
with which materials they give a coat of rough-cast to the 
exterior also. When the dam passes across a running stream, 
they make it convex towards the current; by which it is 
caused to possess much greater strength than if it were 
straight. This dam is usually eleven or twelve feet across 
at its base, and is enlarged every year ; and it frequently 
becomes covered with vegetation so as to form a kind of 
hedge. 

" When the dam is completed, the community separates 
into a certain number of families; and the beavers then 
employ themselves in constructing huts, or in repairing 
those of a preceding year. These cabins are built on the 
margin of the water: they have usually an oval form, and 
an internal diameter of six or seven feet. Their walls are 
constructed, like the dam, of branches of trees ; and they are 
covered, on two of their sides, w r ith a coating of mud. 
Each has two chambers, one above the other, separated by a 
floor; the upper on.- serves as the habitation of the beavers, 
and the lower one as the magazine for the store of bark, 
which they lay up for their provision. These chambers have 
do other opening than one by which they pass out into the 

u li Int.- been said that the Bat oval tail of the beavers serves 
them as a trowel, and is need by them in laying on the mud 
of which their houses are partly composed : hut it does not 
appear that they use any other implements than their incisor 



300 PHYSIOLOGY AKD HYGIEKE. 

teeth and fore-feet. With their strong incisors they cut 
down the branches and even the trunks of trees which may- 
be suitable ; and by the aid of their mouths and fore-feet, 
they drag these from one place to another. 

" When they establish themselves on the bank of a running 
stream, they cut down trees above the point where they in- 
tend to construct their dwellings, set them afloat, and, profit- 
ing by the current, direct them to the required spot. It is 
also with their feet that they dig up the earth they require 
for mortar, from the banks or from the bottom of the water. 
These operations are executed with extraordinary rapidity, 
although they are carried on only during the night. When 
the neighborhood of man prevents the beavers from multi- 
plying to the degree necessary to form such associations, 
and from possessing the tranquillity which they require for 
the construction of the works just described, they no longer 
build huts, but live in excavations in the banks of the 
water/ 5 

407. Blindness of Instinct Exemplified. — 
Instinct moves straight on to its result, and it does so 
blindly. It exercises no intelligence in regard to the pur- 
pose for which the result is intended, or the circumstances 
which tend to defeat this purpose. It evidently in some 
cases never knows any thing of the purpose aimed at by its 
acts, as, for example, when an animal makes provisions for 
a progeny which it is never to see. 

" It is scarcely possible," says Carpenter, " to point to any 
actions better fitted to give an idea of the nature of instinct, 
than those which are performed by various insects when 
they deposit their eggs. These animals will never behold 
their progeny ; and can not acquire any notion from ex- 
perience, therefore, of that which their eggs will produce ; 
nevertheless they have the remarkable habit of placing, in 
the neighborhood of each of these bodies, a supply of aliment 
fitted for the nourishment of the larva that is to proceed 
from it; and this they do, even when they are themselves 
living on food of an "entirely different nature, such as would 
not be adapted for the larva. 






MAX AXD THE INFERIOR ANIMALS. 301 

"They can not be guided in such actions by any thing like 
\ m : for the data on which alone they could reason cor- 
rectly, are wanting to them; so that they would he led to 
conclusions altogether erroneous if they were not prompted 
by an unerring instinct, to adopt the means best adapted 
for the attainment of the required end." 

40S. Result 8 of Instinct mingled with those 
of lira so it. — The results of reason are often mingled with 
those of instinct in such a way that it is difficult to distin- 
guish them from each other. But instinct is of itself wholly 
irrational. If it were not so, it would avoid acting when- 
ever action would evidently be useless. But instinct has 
not the eves of reason to see when this is the case. It leads 
the animal blindly on ; so that, although under all ordinary 
circumstances the object is accomplished definitely and in 
the best manner, yet there is no capability of making pro- 
vision for extraordinary circumstances. Therefore, actions 
are occasionally performed which do not at all answer the 
purpose which the instinct is designed to effect. 

Instinct, though perfect in its action under the uniform 
circumstances under which it is destined to act, is a kind of 
blunderer when irregular circumstances arise. Instinct is a 
strict routinist, while reason readily accommodates itself to 
endlessly varying circumstances. In illustration of the 
e characteristic of instinct, take a few examples: 

The hen will sit on pieces of chalk shaped like eggs, 
adily a- Bhe will sit on the eggs themselves. The flesh- 
fly often lays its eggs in the carrion-flower, the odor of which 
i much like that of tainted meat as to deceive the insect. 

40U. Blindness of Instinct Illustrated in 
the Jieacer. — An amusing illustration of the blind disre- 
gard of circumstances in following out the promptings of 
instinct is given by a gentleman, Mr. Rroderip, in an ac- 
count of a beaver which he caught when very young. As 
as it was Lei out of its cage, and materials were placed 
in itsway.it began to build after the fashion followed by 
timals when they construct their dam in a stream 
of water and build their habitations in its banks. " Even 



302 physiology a^d hygieke. 

when it was only half grown," says Mr. B., " it would drag 
along a large sweeping-brush, or a warming-pan, grasping 
the handle with its teeth, so that the load came over its 
shoulder ; and would endeavor to lay this with other ma- 
terials, in the mode employed by the beaver when in a state 
of nature. The long and large materials were taken first ; 
and two of the largest were generally laid crosswise, with 
one of the ends of each touching the wall, and the other 
ends projecting out into the room. The area formed by the 
cross-brushes and the wall, he would fill up with hand- 
brushes, rush-baskets, books, boots, sticks, cloths, dried turf, 
or any thing portable. 

" As the work grew high, he supported himself on his tail, 
which propped him up admirably ; and he would often, after 
laying on one of his building materials, sit up over against 
it, appearing to consider his work, or as the country people 
say, ' judge it/ This pause was sometimes followed by 
changing the position of the material judged ; and sometimes 
it was left in its place. After he had piled up his materials 
in one part of the room (for he generally chose the same 
place), he proceeded to wall up the space between the feet 
of a chest of drawers which stood at a little distance from it, 
high enough on its legs to make the bottom a roof for him ; 
using for this purpose dried turf and sticks, which he laid 
very evenly, and filling up the interstices with bits of coal, 
hay, cloth, or any thing he could pick up. 

"This last place he seemed to appropriate for his dwelling ; 
the former work seemed to be intended for a dam. When 
he had walled up the space between the feet of the chest of 
drawers, he proceeded to carry in sticks, cloths, hay. cotton, 
&c, and to make a nest ; and when he had done, he would 
sit up under the drawers, and comb himself with the nails 01 
his hind feet." If the instinct of this animal had been at 
all rational, it would not have impelled him to construct a 
dam and a dwelling in a common room, where they would 
be of no use to him. Eeason would have dictated the build- 
ing of a nest and nothing more. 

410. Care for Progeny. — The care which animals 



MAX AND THE INFERIOR ANIMALS. 303 

exercise in relation to their progeny seems to be governed 
to a great extent, perhaps wholly, by a blind instinct. All 
care is given up when care is no longer needed, and with it 
what appears to be affection is given up also. In animals 
there is no such lasting affection of the parent for the pro- 
geny as there is in man ; for in them it is merely instinc- 
tive, and not rational and moral in its character, and it, 
therefore, lasts only so long as it is needed to carry out the 
purposes for which this particular instinct is designed. In- 
deed, in some cases there can be no affection in all the care 
which is instinctively exercised by the parent, for it is put 
forth for progeny which the animal is destined never to see. 

And in those cases among animals in which the family 
state exists, it is a mere temporary affair, and as soon as the 
offspring is able to take care of itself it is no more to the 
parent than any other animal of the same tribe is. 

411. Some Animals have Intell lf/enee as 
irell as Inst hi et. — When this intelligence is shown in 
the mere power of imitation it is of a low order. The par- 
rot that learns to imitate man in speech is not nearly so 
intelligent as some animals that have no such power. Some 
animals have really a reasoning intelligence — that is, they 
make rational inferences. Their reasoning is sometimes, 
as before remarked, so mingled with the operations of in- 
stinct, that it is difficult to distinguish them accurately. 

In the case of the beaver, who labored so faithfully in 
obedience to a blind instinct, there was some exercise of 
reason, as, for example, when he "judged" his work. But 
it is difficult to point out definitely the line between instinct 
and reason in such a case. There are some animals, how- 
ever, in whom the workings of a reasoning intelligence are 
t<» be seen with perfect distinctness. But their reasoning 
differs from that of man. 

The inferences which the reasoning animal makes are 

individual : while man goes beyond this, and makes 

ral inferences, and therefore discovers general truths. 

ton's dog Diamond, saw apples fall to the ground, as 

well a.- his master. And he was capable of making some 



304 PHYSIOLOGY AND HYGIENE. 

inferences in regard to them ; but they were individual 
inferences. 

For example, if an apple-tree were shaken, and the dog 
were hit by a falling apple, whenever he saw other apples 
falling he would infer that he might be hit again, and 
would infer also that it was best for him to get out of 
harm's way. This would be the extent of his reasonings. 
But his master inquired into the cause of the fall of the 
apple, and by considering this and other similar phenomena, 
he deduced general principles, which govern the movements 
both of the atoms and the worlds of the universe. 

The inferences which are formed by animals are mere 
results of the association of ideas, and the process, there- 
fore, really hardly merits the appellation of reasoning. 
Thus, in the case of Newton's dog, supposed above, the 
idea of the falling apples was associated in his mind with 
the hurt experienced when he was hit, and prompted the 
getting out of harm's way. 

When such associations are extended and complicated, it 
appears at first thought as if the animal acted in view of 
general truths arrived at by the same process of reasoning 
that man employs. But it is a mere extension of mental 
associations. Thus, Newton's dog probably associated the 
idea of being hit and hurt with other falling bodies beside 
apples. And so, too, various circumstances might come to 
be associated with the falling of bodies, and thus complicate 
the mental process which occurred when he saw any object 
falling near him. 

412. Reasoning in Animals mere Mental 
Association. — To show somewhat the extent to which 
this mental association operates in the brute mind, some 
examples will be given. A wren built its nest in a slate 
quarry, where it was liable to great disturbance from the 
blastings. It soon, however, learned to quit its nest and fly 
off to a little distance, whenever the bell rang to warn the 
workmen previous to a blast. As this was noticed, the bell 
was sometimes rung when there was to be no blast, for the 
sake of the amusement in seeing the poor bird fly away 



MA^T AXD THE INFERIOR ANIMALS. 305 

when there was no need of alarm. At length, however, it 
ceased to be deceived in this way, and when it heard the bell 
ring it looked out to see if the workmen started, and if they 
did, then it would leave its nest. 

In this case the bird merely learned to connect in its 
mental associations two circumstances with the blasting, 
instead of the one from which it at first took the warning. 
The operation of this mental association is shown in a little 
different manner in the following case : 

Some horses in a field were supplied with water in a 
trough which was occasionally filled from a pump. As the 
supply was not always sufficient, one of the horses, more 
sagacious than the rest, whenever he, on going to drink, 
found the trough empty, pumped the water into it by tak- 
ing hold of the pump-handle with his teeth, and moving 
his head up and down. The other horses seeing this, would, 
whenever they came to the trough and found it empty, tease 
the one that knew how to pump, by biting and kicking 
him till he would fill the trough for them. 

In this case the horse that did the pumping associated in 
his mind the motion of the pump-handle, as he had seen it 
done by his master, with the supply of water. And while 
they associated this supply with his pumping, he knew what 
their teasing him meant, because he associated it with their 
motions about the trough, indicating so plainly that what 
they wanted was water. 

A dog belonging to a Frenchman was observed to go 
every Saturday, precisely at two o'clock, from his residence 
at Loeoyarne to Hennebon, a distance of about three-quar- 
ters of a league. It was found that he went to a butcher's, 
and for the purpose of getting a feast of tripe which he 
could always have at that hour on Saturday, their day of 
killing. It is also related of this dog, that at family prayers 
be was always very quiet, till the lost paternoster was com- 
menced, and then lie would uniformly get up and take his 
station near the door, in order to make his exit immediately 
on its being opened. 

The narrator of these facts thinks that the first fact shows 



306 PHYSIOLOGY AND HYGIENE. 

that the dog could measure time and count the days of the 
week. But this can not be so. The dog undoubtedly asso- 
ciated in his mind the time at which he could get the tripe 
with something that occurred on Saturday at that hour at 
his master's house, just as he associated the concluding of 
family prayers with something that occurred as the last 
paternoster was read, perhaps with some peculiarity in the 
manner of his master when he came to that part of the 
service. 

413. Relation between Cause and Effect 
learned from Association. — Animals learn the rela- 
tion between cause and effect by this mental association, and 
act upon the experience thus gained. This is manifest in the 
examples cited. And it may be observed in many acts that 
we witness occasionally in the higher animals. Thus, for 
example, as a horse was cropping some grass, he took hold of 
some that was so stout, and yet so loosely set in the ground, 
that he pulled it up by the roots, and, as the dirt which wi 
on it troubled him, he very deliberately knocked it across 
the bar of a fence till he got all the dirt out, and then went 
on to eat it. 

Here was a knowledge of cause and effect which was 
derived from previous experience through mental associa- 
tion. You see the same thing when you see a cat jump up 
and open the latch of a door, or a horse unbolt the stable 
door to get out to his pasture. But in all such cases the 
knowledge of cause and effect differs from the same knowl- 
edge in man in one important particular. In the animal it 
is always an individual knowledge, that is, a knowledge of 
individual facts ; while in man it is often a knowledge which 
has relation to general truths or principles. 

From the facts stated in the last few paragraphs, it is 
clear that Carpenter is not correct in saying that "the 
mind of man differs from that of the lower animals rather 
as to the degree in which the reasoning faculties are de- 
veloped in him, than by any thing peculiar in their kind? 
While there is much in common between them in their 
modes of mental action, especially if man be compared with 



j 



MAX AXD THE INFERIOR ANIMALS. 307 

other animals in the period of his infancy and childhood, 
there is, as you have seen, one attribute of the human mind 
which is wholly peculiar to it, and never exists in any degree 
in any other animal. And this attribute, the power of ab- 
stract reasoning, or in other words, the power of deducing 
general truths or laws from collections of individual facts, 
constitutes the great superiority of the human mind, in dis- 
tinction from the mind of the brute. 

414. Language. — It is this attribute which is the 
source of language in man. This can be readily seen by 
observing what is the nature of language. It is a collection 
of corresponding vocal and written signs of an arbitrary 
character, arranged according to certain general rules or 
principles. Other animals do have a kind of language of a 
very limited character. It is the language of natural signs. 
It is composed of cries and motions, which vary in different 
tribes of animals, so that each tribe may be said to have its 
own natural language. But animals never invent and agree 
upon any arbitrary signs, as is done continually by mankind 
in the construction and extension of language. This they 
can not do, because abstract reasoning is required for such 
an invention. General principles are observed in the con- 
struction and arrangement of arbitrary signs, and, as has 
been shown, brutes know nothing of principles. 

415. The Source of Man's Belief in a Crea- 
tor. — If he had not the power of deducing general truths 
from individual facts, he could neither discover the truth that 
there is a first great Cause, nor appreciate or even receive it, 
if it were communicated to him. Not the faintest shade of 
such an idea can he communicated to any of the inferior 
animals, however high their mental manifestations may be, 
and simply because the structure of their mind is such that 
they know nothing of general principles. 

trpenter speaks of the disposition to believe in the exist- 
• an unseen bur powerful Being, which is found to 
be tmiversa] even among the mosl degraded races of* man- 
kind, as a natural tendency, which be seems to think is im- 
planted in the human breast by the Creator. But it ap- 



308 PHYSIOLOGY AtfD HYGIENE. 

pears clear, that it is a mere natural result of the exercise of 
the power that has just been mentioned. 

416. Conscience. — Man differs from other animals 
also in having a conscience, or a knowledge between right 
and wrong, and a sense of obligation in relation to it. This 
moral sense is supposed by some to be a mere result of the 
exercise of the power of abstract reasoning. But others 
suppose that the sense is implanted as a distinct quality or 
power, and that the office of the reasoning power in relation 
to it is to bring the evidence before it for its decision. 

This point will not be discussed, but that there is no doubt 
as to the existence of such a sense in man. Some attempt 
to throw doubt over it by pointing to its perversions, main- 
taining that it is a mere creature of circumstances, varying 
almost endlessly in different parts of the world. But it 
would be just as rational to attempt to show that there is no 
such thing as a sense of the beautiful in man, by appealing 
to the evidences of perversions of taste, which ignorance, 
bad education, and foolish and novelty- loving fashion have 
induced. 

417. None in Animals. — In those cases in animals 
in which this moral sense has been supposed to exist, it is 
nothing but slavish fear. It has been said by some one that 
man is the god of the dog ; but it is trifling with what is sacred 
to compare the attachment of an animal to its master and 
its fear of his displeasure, with the intelligent regard of man 
for his Creator as a holy and benevolent being. We ordi- 
narily recognize the distinction between man and animals, as 
to the existence of a conscience, in the language we use. 

We never attach the idea of moral character to the acts of 
an animal except by the force of association, and then only 
slightly and loosely. We are not apt to speak of punishing 
a dog, for this word implies a moral fault as the occasion of 
the infliction. We ivhip him, sometimes, simply to associate 
in his mind the smart with the act done, so as to prevent 
him from doing it again, and sometimes to vent our ill feel- 
ing for the harm done us on the poor dog that has so innc 
cently done it. 



at 



■o. 



MAN AND THE INFERIOR ANIMALS. 309 

It is related of Sir Isaac Newton that he had a favorite 
little dog called Diamond, who being left in his study, 
overset a candle among his papers, and thus burnt up the 
almost finished labors of many years, and yet the philosopher 
only said, " Diamond ! Diamond ! thou little knowest the 
mischief thou hast done." Newton was a wise and good 
man, and while he saw that whipping the dog would do no 
good in preventing any similar accident in the future, he 
had no ill feeling to vent on poor Diamond, who certainly 
had a better and more rational master than most dogs have. 

418. Summary of Mental Distinction. — The 
mental distinction between man and animals may be thus 
summed up. The animal is governed by instinct, and in 
the higher orders by a kind of reasoning which is based 
upon mental association. Man has, in addition to instinct 
and this lower order of reasoning, the power of abstract 
reasoning. In the lower orders of animals probably instinct 
rules alone. In them there is none even of the limited 
reasoning which we see in the higher animals. They have 
a nervous system with certain central organs, but have really 
no one great central organ that we can call the brain. As 
we trace the animal kingdom upward, we soon find that a 
brain appears, that is, such an organ as may be considered 
the chief center of the nervous system. When we come to 
man the brain is much larger than in any other animal, and 
his intelligence is not only greater, but it is of a different 
character. Xot only is the amount of his reasoniug by 
ciation greater than in other animals, but there is also 
superadded, as his grand distinguishing mark, the power of 
abstract reasoning. 



; 



310 PHYSIOLOGY AND HYGIENE. 

CHAPTER XIX. 

VARIETIES OF THE HUMAN RACE, 

419. Mankind all the Same Species, but Pre- 
senting very marked Varieties. — Although, as we 
look at men of different nations, we find that there is a 
general agreement in form and organization, there are many 
points in which they strikingly differ from each other. 
" With those forms, proportions and colors," says Mr. Law- 
rence, " which we consider so beautiful in the fine figures 
of Greece, contrast the woolly hair, flat nose, thick lips, re- 
treating forehead, advancing jaws, and black skin of the 
negro ; or the broad square face, narrow oblique eyes, 
beardless chin, coarse straight hair, and olive color of the 
Oalmuck. 

Compare the ruddy and sanguine European with the jet- 
black African, the red man of America, the yellow Mon- 
golian, or the brown South Sea Islander; the gigantic 
Patagonian to the dwarfish Laplander; the highly civilized 
nations of Europe, so conspicuous in arts, science, literature, 
in all that can strengthen and adorn society, or exalt and 
dignify human nature, to a troop of naked, shivering, and 
f starved New Hollanders, a horde of filthy Hottentots, or 
the whole of the more or less barbarous tribes that cover 
nearly the entire continent of Africa; — and although we 
must refer them all to the same species, they differ so re- 
markably from each other as to admit of being classed into 
a certain number of great varieties ; but with regard to the 
precise number, naturalists have differed materially." 

Ouvier admitted but three varieties, the Caucasian, 
Negro, and Mongolian. The more commonly received 
classification, however, is that of Blumenbach, who makes 
five varieties, viz., the Caucasian, Ethiopian, Mongolian, 
American, and Malay. 



VARIETIES OF THE HUMAN RACE. 311 

420. Caucasian. — The chief characteristic of the 
Caucasian variety is the line form of the head, it being 
nearly oval, as you view it from the front. It is also char- 
acterized by a great range of variations of the color both of 
the skin and the hair. There has been more of civilization 
and improvement of every kind in this race than in any of 
the others. It is mentally superior to the other races. 
It is called Caucasian from Mount Caucasus, from the 
vicinity of which, it is supposed, it originated. Even at the 
present day it is said that the characteristics of this race are 
most perfectly developed in the Georgians and Circassians, 
who live in the neighborhood of this range of mountains, 
and who are considered the handsomest people in the world. 

421. The JEthiojtian Variety. — The organization 
has not the perfection and elegance which the Caucasian 
presents, and it shows an approximation to the higher 
orders of the inferior animals. The skull is small. The 
forehead is retreating, while the face below is projecting, 
the cheek bones being prominent, and the nose broad. The 
apparatus of the senses is thus fully developed, while the 
brain is less than in the Caucasian. The hair is black, oily, 
and frizzled. It is commonly said to be woolly, but it is 
really not so. Dr. Carpenter says that "microscopic exam- 
ination clearly demonstrates that the hair of the negro has 
exactly the same structure with that of the European, and 
that it does not bear any resemblance to wool save in its 
crispiness and its tendency to curl." The skin is generally 
black ; but not so in all the race, for the Caffirs and the 
Hottentots are yellow. 

422. The Mongolian Variety. — The Chinese race 
forms the largest family and is characterized by prominent 
broad cheek bones, flat square face, small oblique eyes, 
Straight black hair, scanty heard, and olive skin. 

42 3 » The American Variety. — Characterized by 
high cheek bones, a narrow low forehead, features large and 
bold. which are deeply sunken in large 

socket-,, hair generally black, stiff and straight, and com- 
plexion varying from a crimson brown to a deep copper. 



312 PHYSIOLOGY AND HYGIENE. 

4:24:. The Malay Variety.— This variety occupies 
the Islands south of Asia, in the Indian and Pacific oceans, 
and has not so well marked characteristics as the other varie- 
ties. The complexion is brown, varying from a light tawny 
to almost black, the hair is black and thick, the forehead 
is low and round, the nose is full and broad, the nostrils 
wide, and the mouth large. 

425. Differences in Individuals, Families 
and Nations— produced by Similar Causes. — 
The national differences are evidently produced by causes of 
very much the same character with those which produce 
differences in individuals and families. And the question 
arises whether such differences as those which Blumenbach 
describes as marking the races, are not produced in a similar 
manner. This question has been much discussed, and there 
is great difference of opinion in regard to it. The great 
majority of naturalists believe in the unity of the origin 
of the human race, and hold that its varieties are the results 
of the various circumstances by which man has been sur- 
rounded. 

But some suppose that the different varieties come from 
separate pairs created by God in different localities, and 
hold that the history in Genesis is a history of the origin 
of only one of the varieties of the race. Those who advo- 
cate this doctrine are few in number ; but it has acquired 
greater currency of late, because one of the most eminent 
naturalists, Professor Agassiz, espoused it. 

426. Views of I*rof. Agassiz.— All animals, he 
asserts, like plants, have particular localities, for which they 
are fitted, and to which they belong. The zoological prov- 
inces, as he terms them, are of unequal extent, some ani- 
mals having a wider range than others. From this general 
law of distribution, which he illustrates with many facts, he 
infers that the various animals on the face of the earth were 
not created in one part of the earth and distributed from 
this to other parts, but were created in the provinces to 
which they belong. 

This view of the subject forces itself upon the mind of 






VARIETIES OF THE HUMAN RACE. 313 

the naturalist, as he observes the arrangement of the various 
tribes of animals on the earth's surface. And besides, 
there are apparently insurmountable difficulties in the way 
of a diffusion of animals over the globe by means of migra- 
tion. For example, we can not conceive how the polar 
animals could have migrated over the warmer tracts of 
land, which they would have to cross according to this sup- 
position, for, with the greatest precautions, i£ is impossible 
now to keep them alive in such circumstances. 

And farther, some animals of the same species, some- 
times presenting varieties and sometimes not, are found in 
different localities, which are so cut off from all communi- 
cation with each other that it is impossible that these 
animals could migrate from some one locality to all the 
rest " To assume," he remarks, " that the geographical 
distribution of such animals, inhabiting zoological districts 
entirely disconnected from one another, is to be ascribed to 
physical causes, that these animals have been transported, 
and. especially, that the fishes which live in fresh water 
basins have been transported, from place to place — to sup- 
pose that perch, pickerel, trout, and so many other species 
found in almost every brook and every river in the tem- 
pi-rate zone, have been transported from one basin into 
another by freshets or by water-birds — is to assume very 
inadequate and accidental causes for general phenomena." 
Not only then were different species of animals created 
originally in different localities, but it is also true, to a con- 
siderable extent, that animals of the same species occupy- 
ing different localities were created in those localities. 

All this he claims to be consistent with scripture, and 
with very good reason. The account of the preservation 
of animals in the ark. interpreted according to the common 
license of language, indicates really only such a preserva- 
tion as would be n for the stocking of that pari 
he world where Noah and his family were, after the 
waters should subside. The number ami the variety of 
the animals preserved for this purpose would of course 
id would, according to the common usage 
14 



314 PHYSIOLOGY AND HYGIENE. 






of language in narration, be spoken of in the terms 
used in the Bible. This interpretation holds equally, 
whether the deluge be considered as haying been partial or 
universal. 

The case being thus quite clearly made out in relation to 
animals generally, he proceeds to trace an analogy between 
them and the races of man in this respect. He supposes 
that there are certain zoological provinces for the different 
human races, as there are for the different species and 
varieties of animals ; and that these races were separately 
created in these provinces with organizations suited to their 
peculiar localities. While he allows that climate and other 
influences affect the varieties of the human race, he claims 
that they alone are not competent to produce them, and he 
infers, therefore, that there must have been, as in the case of 
animals, different original creations in the different zoologi- 
cal districts. He accordingly claims that the history given 
in Genesis is a history of the origin of only one branch of 
the human family. He does not suppose that the different 
branches constitute different species, but are made varieties 
of one species.* 

He characterizes mankind as being every where essentially 
the same in mental character, and alike the accountable 
subjects of God's kingdom, notwithstanding their multiple 
origin. It is in this respect that he considers them as being 
of one brotherhood, and he looks upon the expression in 

* The difference between species and varieties is this : The distinc- 
tion of species rests upon specific characteristics, that can not be 
changed by those influences which tend to produce the differences that 
make varieties. The characteristics of a species are original, while 
those of a variety are acquired. " The term species," says Prichard, 
"includes only the following conditions, namely, separate origin and 
distinctness of race, evinced by the constant transmission of some 
characteristic peculiarity of organization. A race of animals or of 
plants marked by any peculiarity which it has ever constantly dis- 
played, if termed a species ; and two races are considered specifically 
different, if they are distinguished from each other by some charac- 
teristic which the one cannot be supposed to have acquired, or the 
other to have lost, through any known operation of physical causes." 






VARIETIES OF THE HUMAN RACE. 315 



the Bible, "made of one blood/' as being entirely fig- 
urative, and as referring to " the higher unity of man- 
kind, and not to their supposed connection by natural de- 
scent." 

We will not go into a thorough discussion of this ques- 
tion, as it is not possible in the narrow limits of a chapter. 
Only a general view of the chief facts and arguments that 
bear upon the point at issue will be presented. Let us look 
at this subject first in the light of physiology and natural 
history. 

The great majority of physiologists and naturalists, as 
has been remarked, have thus far been of the opinion 
that the human race came from one origin, and that the 
varieties of it have been produced by the various influences 
to which man has been subjected. These are commonly 
included in the general expression, climatic and other influ- 
ences. To be more particular, they are — climate, situation, 
food, clothing, customs, habits, state of civilization. 

Too great prominence has been undoubtedly given to the 
influence of climate. Lawrence very justly remarks in his 
general conclusions in regard to the production of the 
varieties in man and animals, " that of the circumstances 
which favor this disposition to the production of the varie- 
ties in the animal kingdom, the most powerful is the state 
of domestication" This word, as he uses it, includes all 
those social influences, which as manifestly affect the ani- 
mals which man domesticates as they do man himself. 
The analogy between man and animals in relation to the 
results of the influences referred to, will be spoken of more 
particularly. 

That climatic and other influences do have a very great 
agency in producing the varieties, both individual and gen- 
eral, that we see on looking over the human family, no one 
doubts. The only question is, whether they have produced 
all these differences — whether, for example, they have 
occasioned that very wide difference that we see between 
the Caucasian and the Ethiopian. These limits will not 
allow us to go into a full examination of the influence of 



316 PHYSIOLOGY AXD HYGIEXE. 

these causes, and only a few points will be noticed in a 
very general way. 

427* Color Affected by Climate. — That climate 
has a great influence upon the color of the race is proved 
by many clearly observed facts. Tropical heat always has 
a tendency to produce a black skin. This is shown very de- 
cidedly in the case of the Jews, who have preserved their 
characteristic features amid varieties of climate, and yet 
have their color altered. 

Thus, while the Jew of the interior of Europe has a fair 
complexion and light hair, under the scorching sun of 
India his hair is crisped, and his skin is black. The evi- 
dence of the influence of climate is the stronger in this 
case, because the change from the original color has been 
twofold. For the original Jew in Palestine had undoubt- 
edly a dusky skin and dark hair, upon which the temperate 
climate of the interior of Europe and the tropical climate 
of India have produced two opposite effects. 

428. Civ cum stances Affecting the Form. — 
But in the varieties of the human race there are differences 
of form as well as of color. That the various influences to 
which man is subjected have a marked effect upon his 
physical form is universally acknowledged. We see this 
alike in individuals, families, and nations. Intellectual and 
moral influences manifestly have some agency in moulding 
the shape of the head in the individual. The differences 
which we so commonly see in the shape of the head between 
the intellectual and the ignorant, are not owing altogether 
to original difference of capacity, but in part to education. 

The brain, like all other organs in the body, is influenced 
in its development by the degree of activity to which it is 
stimulated. It is not made an exception to this general law 
of development. Accordingly we find that depressing in- 
fluences tend to make the top of the head, the cerebral 
part, small, and the forehead retreating, while the face, 
from the predominance of the sensual over the intellectual, 
is rendered relatively too prominent. The tendency of 
elevating influences is of an opposite character. And 



1 

: 



VARIETIES OF THE HUMAN RACE. 317 

such influences, thus operating in the individual, when 
repeated and accumulated from generation to generation, 
produce great and lasting results. It is thus that a race 
becomes either degraded or elevated. By a continuance and 
accumulation of influences it acquires either a good or a 
bad tixed character. 

One class of causes effecting changes in the physical 
form lias been mentioned, the influence of which is mani- 
fest. But there are changes seen, the causes of which we 
cannot clearly make out ; and yet we know that they are 
occasioned by the varying circumstances in which man is 
placed. By the compound influence of many causes com- 
bined we continually see introduced differences in the 
shapes of various parts of the body. Family and national 
peculiarities are thus occasioned. The influences to which 
we have thus referred, some of which are little understood, 
are all those which Mr. Lawrence includes in the term 
domestication, which, as before said, he applies to man as 
well as to animals. 

429. Marked Tendencies to Three Different 
Forms of the Head. — Dr. Prichard has pointed out 
three different types of form in the head, occasioned by three 
distinct classes of influences. One he terms the prognathous 
(a word derived from two Greek words meaning before and 
the jaw), in which the jaws project very prominently for- 
ward. This formation is characterized by the predomi- 
nance of the sensual over the intellectual, the apparatus of 
the being largely developed, while the cerebrum is 

small, making the forehead retreating. 

The tendency to assume this type is always in proportion 
to the action of the degrading influences. "Want, squalor, 
and ignoran arpenter, "have a special tendency 

the diminution of the cranial portion of the 
skull, and that increase of the facial, which characterize 
prognathous type." It is seen most strongly marked 
in the of the Gold Coast. 

In the pyramidal type, as ii is termed, the cheek bones 
are very broad, and the above are so shaped as to 



318 PHYSIOLOGY AND HYGIENE. 



rViic 



give the top of the head a sort of pyramidal form. This 
type we see in those tribes that lead a wandering life — the 
nomadic races, as they are called. 

The oval or elliptical form, which is seen so well marked 
in the Caucasian variety, is manifestly the result of eleva- 
ting influences. These types are convertible into each 
other. Thus, the oval may be degraded into the prog- 
nathous, or the prognathous may be elevated into the oval. 
The latter change is seen in the Ethiopian, when in suc- 
cessive generations he is subjected to elevating influences, 
in his intercourse with the Caucasian. And it is interest- 
ing to observe that the form of the head is more readily 
changed than the color. 

"Thus," says Carpenter, "in some of the older West 
Indian colonies, it is not uncommon to meet with negroes, 
the descendants of those first introduced there, who ex- 
hibit a very European physiognomy ; and it has even been 
asserted that a negro belonging to the Dutch portion of 
Guinea may be distinguished from another belonging to 
the British settlements, by the similarity of the features 
and expression in each to those which peculiarly charac- 
terized his master's. The effect could not have been pro- 
duced by the mixture of bloods, since this would be made 
apparent by alteration of color." In the same way is the 
pyramidal type convertible with the others. The pyramidal 
and the prognathous are often mingled together, by the 
influence of vagabond habits and degrading causes. 

430. Insensible Gradations in Diversity. — 
The view thus given of the operation of influences in pro- 
ducing the varieties of mankind is strengthened by the 
fact that, as Humboldt says in his Cosmos, there are 
"many intermediate gradations in the color of the skin 
and in the form of the skull." If we look alone at the 
extremes in varieties of color and form, we are of course 
disposed to regard such great differences as marking a dis- 
tinction of species. But when we see these varieties pass- 
ing into each other by such insensible gradations, and at 
the same time observe the manifest influence of causes 



VARIETIES OF THE HUMAN RACE. 319 

upon these gradations, as in the cases referred to in the last 
paragraph, the evidence is clear to us that the varied influ- 
ences brought to bear upon man are competent to produce 
the varieties of the race. 

431. Fi, redness of the Varieties. — But it is 
objected that, although climatic and other influences have 
a great eftect. yet, so far as we can see, they only produce 
changes that approximate to those differences that mark 
the grand divisions of the race. They cannot, for example, 
be shown, from actual observation, to have effected the 
entire change in any length of time of any portion of the 
Caucasian race into the Ethiopian, and, on the other hand, 
of the Ethiopian into the Caucasian. It is objected, farther, 
that the peculiarities of the principal varieties of man 
existed in the early history of the race. This appears in 
relation to the Ethiopian variety in the figures found on 
Egyptian monuments. These show that the peculiarities 
of the negro race were as strongly marked nearly 5,000 
years ago as they are now. This fixedness of character 
under such a variety of influences continued so long, it is 
claimed, indicates that the peculiarities w^ere original, and 
not acquired. 

In reply to both of these objections, your attention is 
called to a general fact, which is deemed very significant in 
its bearing upon the great point at issue. It is the fact 
that when a variety is formed by any influences, either 
among plants or animals, it is apt to remain in spite of 
opposing influences. It seems to be easier by far to produce 
a variety, than to bring it back to the character of the 
original from which it came. 

432. Influence of Domestication both in 
31/rn and in An t mats. — Domestication has been 
continually producing varieties in the animals that man 
has bo largely appropriated to his service, and the varieties 
once produced commonly remain. And the same thing is 
seen in the varietiee resulting so continually in the human 
race from the same class of influences. It is matter of 
common observation that family and national peculiarities 



320 PHYSIOLOGY AND HYGIENE. 

are apt to be perpetuated. And it is not merely from a 
continuance of the causes from which they result, for they 
are apt to remain even when strong counteracting influ- 
ences are brought to bear upon them. 

Now the causes which tend to produce varieties in the 
human race acted of course at the first, and during the 
first ages of the race were competent to produce the most 
prominent varieties. And the tendency to fixedness, which 
we see exemplified in so many ways in the varieties of both 
plants and animals, is sufficient to account for the per- 
petuation of such marked characteristics as those of the 
Ethiopian and the Caucasian. 

The analogy then which is thus observed between man 
and the domesticated animals is a much clearer and 
stronger one than that which Professor Agassiz has at- 
tempted to make out between man and animals generally 
in regard to zoological districts. And the inference is a 
legitimate one, that the same influences that we see pro- 
duce varieties in domesticated animals, are competent to 
produce the varieties in the human race, which are even 
less marked than some of those which we see in animals. 
Varieties are produced more readily and in greater numbers 
in animals than in man, probably because they have less 
power of resisting influences that act upon them. The varie- 
ties of some of the domesticated animals are very numerous. 

The analogy drawn between man and animals in regard 
to zoological districts is weakened by the consideration 
that there was no necessity for man's being created in dif- 
ferent localities, because he can migrate so easily from one 
country to another. The necessity existed in regard to 
plants and animals, but not to the same extent in all. Mi- 
gration is easier in the case of some than in the case of 
others. And this difference seems to have been acted upon 
by the Creator. 

Accordingly, the evidence is quite conclusive, that those 
animals which have been so universally appropriated by 
man to his service, have been diffused from central points 
and have gone with man, instead of being created in many 



VARIETIES OF THE HDIA^ RACE. 321 

localities. This being the case, it is hardly to be supposed 
that man, who is capable, through his ingenuity, and skill, 
and daring, of going every where, would be unnecessarily 
created in different pairs at different points on the earth's 
surface. 

433. New Causes Occasionally Introduced 
by the Creator. — But suppose that, in view of all the 
evidence, we should come to the conclusion that the clima- 
tic and other influences are not the sole causes of the differ- 
ences in the races, are we of course driven to the admission 
that, as Agassiz and others teach, there must have been cre- 
ated at the first, several, we know not how many, different 
pairs in different localities ? By no means. We are not to 
forget that the Creator, besides using influences of which 
we have no knowledge (which he is continually doing), can 
effect new combinations of the causes already existing, or 
introduce into operation entirely new causes. That he is 
from time to time evolving new results in one or the 
other of these ways, or both of them, is manifest. 

The very common notion, that at the creation all the 
causes which have produced all the phenomena that have 
been observed to the present time were then set in opera- 
tion, and have been left to work out their results, seems to 
be contradicted by many facts. Most of the causes then set 
in operation, it is true, have been at work ever since. 
Unless this were so, nature would not exhibit the regularity 
which it now does, and calculations could not be made with 
such definiteness as to its processes from knowledge gained 
by experience. But changes and irregularities sometimes 
occur which must have been the result of new causes. A 
few examples only will be given. 

The age of man before the flood was much greater than 
it has been since. A change was effected at that period. 
It was not a mere arbitrary change, but such a change in 
the very character of the human system, that its capability 
of n rhe tendency to decline was greatly reduced in 

the period of its continuance. It was hot a change result- 
ing from the influence of deteriorating causes, for in that 



322 PHYSIOLOGY AND HYGIENE. 

case it would have been less suddenly induced. To effect 
this change some new causes must clearly have been 
brought to bear upon the system, making it in the post 
diluvian a different system in some important respects from 
what it was in the ante-diluvian. 

Take a fact of a different kind, indicating a similar change 
of agency. New diseases from time to time appear. This 
could not occur without either entirely new causes, or new 
combinations of elements heretofore existing. That very 
definitely marked disease, the small-pox, we have the best 
of evidence, was not known to the ancients, but is compar- 
atively a modern disease. It is impossible to conceive of its 
being introduced without some new cause of a very definite 
character. 

Take now another fact of a widely different kind from 
either of those noticed. The earth is marked all over with 
signs of great convulsions that have occurred since its 
creation. It has been supposed till recently that these 
signs all refer to that great event described in the Bible, 
the Deluge of Noah ; but geological researches have demon- 
strated pretty clearly that they point in part at least to 
other previous convulsions. Now these convulsions are not 
to be reckoned as a part of the regular order of nature. 
They could not have resulted from the ordinary causes that 
act continuously. New causes must have been introduced 
at the time, to produce these unwonted results. 

It matters not to the argument above indicated, whether 
the new results that are occasionally developed, come from 
a direct agency at the time, or come from a chain of causes 
set in operation a long time before. The results are new 
results, and come from causes or combinations of causes 
which differ from those that have produced the ordinary 
and regular results which we witness from day to day or 
from year to year. 

Now in like manner can we suppose, if it be necessary, 
that the Creator produced the varieties of the human race 
by adding other and new causes to the ordinary influences 
to which man is subjected. This is a much more probable 



VARIETIES OF THE HUMAN RACE. 323 

supposition than that of the advocates of the multiple origin 
of the race. 

For besides accounting satisfactorily for the facts, and at 
the same time being consistent with the record in Genesis, 
it is more clearly supported by analogical facts than the 
supposition (for it is mere supposition) that the human 
race was created in different localities. And farther, this 
supposition avoids difficulties which attend the other. For, 
if we suppose that the race came from different pairs, it 
would be difficult to decide how many pairs there were. 
Such are the variations of the race in different localities that 
there would be much disagreement as to the number of the 
representative pairs, and their distinguishing characteristics. 

But it may perhaps be said in objection, that we are sup- 
posing a miraculous interposition. Whether it may rightly 
be termed such will not be considered ; but it is just such 
an interposition, or rather, direct agency, as is affirmed by 
the advocates of a multiple creation, differing from it only 
in the time of its occurrence. 

They suppose the direct agency of God to be put forth 
in creation at different points, whether at different times 
they do not say, and this is really quite immaterial ; and we 
suppose the same direct agency to be put forth, but in a 
less marked manner, to produce a change in what has 
been already created. In supposing the direct agency of 
the Deity at all, we go beyond mere physics ; and he surely 
has the power to put forth this agency at such times as he 
pleases.* 

* There seems to be in the minds of some naturalists a great reluc- 
tance to admit at all the direct agency of the Creator, whether it be 
exerted in consonance with the order of nature which he has estab- 
lished, or miraculously in opposition to it. And they would smile 
skeptically at what they would deem the simplicity or superstition of 
Hugh Miller, in referring some narrow escapes which he has had, in 
pursuing his geological researches, to a particular Providence. The 
relation of tin- agency of the great First Cause to second causes, it is 
true, is a mysterious subject ; but it implies no disposition to fathom 
what is unfathomable if we assert that the facts are far from warrant- 
ing us in the belief that this agency has not been exerted since the 
period of the creation, but confined itself to that time. 



324 PHYSIOLOGY AND HYGIENE. 



Che 



Bat the supposition made above is not needed. The 
regular, continuous, natural causes, which have ever op- 
erated upon man, have been competent to produce all the va- 
rieties of the race. And this supposition was only suggested 
as a consideration for those who fail to see that these causes 
have been thus competent; it is a more probable supposi- 
tion than the one offered by Agassiz and otheus to meet 
the difficulty in the minds of such persons. 

434. The Testimony of the Bible to be Re- 
ceived as Evidence. — Thus far this subject has been 
treated chiefly as one of natural history and physiology. 
But is the testimony of the Bible not to be received as a 
part of the evidence ? Is the question to be decided wholly 
on considerations and facts drawn from natural history and 
physiology ? This seems to be the view of some naturalists, 
though the great majority of them are disposed to admit 
the statements of Scripture as evidence. 

It is true that the Bible does not purport to be a philo- 
sophical book. Its language is based on the principles of 
common and not scientific usage, and is so to be interpreted. 
And it should be thus interpreted in relation to the subject 
before us. Its statements on this subject are of the most 
explicit character. It purports to give an account of the 
origin of the race, and portions of its history. It ascribes 
the corrupt character of the race to a fallen parentage. 
This connection of the general corruption of the race with 
the fall of its original pair, however divines and philoso- 
phers may differ in accounting for it, is recognized as a fact 
throughout the whole book of revelation. The testimony 
is definite, and is not to be mistaken. 

The question is, whether it be valid testimony. And if 
the Scriptural record be established, as it is abundantly, by 
both internal and coincident evidence, its testimony in 
regard to the origin of the race is to be received by scien- 
tific men. It can not be set aside by any mere presump- 
tive and analogical evidence drawn from physiology and 
natural history. If actual facts be proved inconsistent with 
the Mosaic history, as properly interpreted, they will of 



LIFE AXD DEATH. 32o 

course bring discredit upon that history. No immunity 
against a strict investigation is to be claimed for the Bible. 
But there is no fear of such an issue ; and it is to be 
remembered that mere analogies are not facts, and are not to 
be deemed as having much force, especially when there is a 
question in regard to their value in comparison with other 
analogies that point to an opposite conclusion. 



CHAPTER XX. 

LIFE AND DEATH, 

43o. Life, though Various in its Manifes- 
tations, in some Senses always the Same. — Life 
is very commonly spoken of as being one thing, although 
its manifestations are exceedingly various in their charac- 
ter. In the simplest growths that Ave see, both in the 
vegetable and in the animal kingdoms, the operations of 
life are in some respects very different from the complicated 

esses that we witness in the human structure, which 
has been the subject of your study in this book. And yet, 
as you have seen in the Chapter on Cell-Life, life in these 
apparently opposite cases is essentially the same. It is the 
same in its origin. It begins always in a single cell, 
whether the living being is to be great or small, simple 
or complex, a plant or an animal, a creature of a day, or 
a being destined to immortality. 

Why it is that from a simple cell the vital force, as it is 
termed, can evolve such a range of diversitied results as we 

in all animated nature, is one of the great mysteries of 

Creator. Aa e in the springtime a bud upon a 

tree unfold gradually, and develop to us successively 

leaves and flowers and fruit, it fills as with wonder when 

reflect how much has come from that little bud ; but 
when we go farther, and think of the whole tree as having 
come from a single cell, so small that it can be seen only 



326 PHYSIOLOGY AND HYGIENE. 

by the microscope, the mystery appears passing wonderful. 
And it is a still greater mystery, when a complicated ani- 
mal organization is looked at as haying been developed by 
the vital force, alike with all other living things, through 
a single cell as its origin. 

Not only is life always the same in its origin, but it con- 
tinues essentially the same in its processes. All the various 
forms which it produces, both in the vegetable and in the 
animal world, are built and kept in repair by cells. All the 
functions, too, are carried on through the same agency. 
The secretions and excretions are effected by constant suc- 
cessive creations of numberless cells. Even the intellectual 
operations in the mind of man are dependent upon cells 
so long as the mind is connected with the body. In think- 
ing, as well as in muscular motion, cells are worn out, and 
must be replaced by other cells, which are continually sup- 
plied by the vital force. 

436. Difference between the Vital Force, and 
Heat, Light, and Electricity. — Life being thus 
wonderful in its operations, the inquiry arises, what can 
this mysterious agent be ? With curious eye we watch its 
workings, but although we can learn some of its laws, its 
nature eludes our search. Then pressing the microscope 
into our service, we trace it back to its hiding-place in a 
minute round cell containing a fluid ; but simple as this 
prison is in which it is confined, it is more of a mystery 
than ever. The vital force, which begins here, and, enlarg- 
ing more and more the sphere of its operations, develops 
gradually the simple or the complicated living form, as the 
case may be, has been classed by some with other forces, 
the nature of which we do not understand, as heat, light, 
and electricity. But it differs from them entirely in some 
important points. While they act in connection with mat- 
ter generally, both organized and unorganized, vital force 
is seen acting only in organized substances. While they 
diffuse themselves through all kinds of matter with more 
or less rapidity, the vital force has no power of diffusion, 
but is confined within certain limits. These limits differ 



LIFE AND DEATH. 327 

in the different living substances. The vital force has the 
power of appropriating matter to itself within these limits. 
It does this by assimilation. It has then the power of exten- 
sion to a limited degree ; while the other forces mentioned 
have the power of diffusion, in some respects limitless. 

Another difference is this. While these forces, light, 
heat, and electricity, are lessened in power by being dif- 
fused, vital force is not lessened by extension. Heat, for 
example, if diffused is lessened at the point of its diffusion; 
but life is as energetic at its starting-point after its exten- 
sion as before, and even more so. It is, so to speak, self- 
generating, while the other forces are mere products. The 
vital force stands peculiarly alone in this respect. The 
effects, too, which this force produces, as it lays common 
matter under contribution, and fashions it in such diversi- 
fied forms, have an infinitely wider range of variety than 
the effects of the other forces. 

437. Life in Blood. — We can thus trace the differ- 
ences between the vital force or principle and other forces, 
but we can not, as before said, discern its nature. We know 
not whether it be one thing. It is convenient to speak of 
it as being so. But we know not but that it may be a 
compound of endowments, or tendencies imparted to mat- 
ter, and varying with the various forms of living substances. 
Some have supposed that the vital principle resides chiefly 
in the blood, and that this is the meaning of the passage 
in the Bible, " the life of the flesh is the blood." That the 
Mood has some vital properties is certainly true. These 
properties are communicated to it as it is made from the 
food, and fit it to be the material for the construction and 
repair of the organization. And it is simply the fact, that 
the blood is the common material out of which all the diversi- 
fied parts of the living structure are made, that is recog- 
nised in the language of Scripture on this subject. The 
same fact is embodied in another form in the remark of 
the French physiologist, that the blood is chair coulante, or 
running flesh. 

438.— Vital Laws Control the Chemical and 



328 PHYSIOLOGY AXD HYGIEXE. 

Mechanical. — When the vital force appropriates to 
itself common matter in assimilation, it takes it away in 
part from the operation of certain forces which have had 
entire control over it. As long as it is common dead mat- 
ter, it is wholly subject to the laws of mechanics, and of 
chemical action. But when it becomes organized living 
matter, the laws of life take possession of it. 

The laws of chemistry and mechanics are not, it is true, 
annulled in relation to it. They still exert their influence, 
but under the control of vital laws. The force of gravity 
acts continually upon the body ; but the living muscles are 
much of the time acting in direct opposition to it. The 
blood circulates on hydraulic principles ; but the vital 
force furnishes the motive pow T er, and keeps the blood 
from becoming solid and stopping up its channels. Chemi- 
cal changes are going on in the stomach, the lungs, and 
at every point in the capillary circulation ; but they are 
modified, controlled, by the vital principle, and are properly 
termed chemico-vital processes. 

The human body is made of materials that are exceed- 
ingly prone to chemical decomposition, and the degree of 
heat which is maintained is such as to favor this result ; 
but the vital force not only holds the chemistry of the 
system in abeyance, but even presses it into its service. 
When life is destroyed, the laws of chemistry assume their 
full sway, and the process of decay begins. 

The very agencies which served, while under the control 
of the vital principle, to maintain the living organization, 
now acting alone, run riot, and work its destruction. Thus, 
that powerful agent, heat, existing in the body at the point 
of 98°, is necessary to the carrying on of the processes of 
life ; but let life be destroyed, and the maintenance of this 
degree of heat would ensure a very rapid putrefaction. So, 
too, a degree of heat which would rapidly putrefy a dead 
egg by quickening the chemical changes, would actively 
stimulate in a living egg those curious vital processes that 
produce at length the bird. During incubation the egg of 
the hen is kept for three weeks at a heat of 105°, and yet 



LIFE AND DEATH. 329 

when the chicken is hatched all of the yolk that is left is 
unchanged. A dead egg would soon putrefy under such a 
temperature. 

439. Change always attends Life in Action. 

— The vital force exhibits its controlling power in an 
extraordinary manner in connection with that great force of 
nature to which reference has just been made. Heat is 
very diffusive, and is exceedingly liable to change from 
varying circumstances. And yet the vital force maintains 
the heat of the body quite uniformly at one point, although 
the agencies which tend to vary it are very numerous and 
effective. The production of heat in the system is a 
chemical operation, but the vital principle regulates the 
quantity in the body very accurately, by providing for its 
escape in various ways, and perhaps by curtailing in some 
measure its production. 

Continual changes are effected by the vital force in every 
part of the body. In one sense death may be said to be 
taking place constantly, while life is as constantly gener- 
ated, as the useless particles are separated and taken away, 
and the new ones are deposited in their place. While these 
changes are going on the vital force so operates as to main- 
tain the peculiar shape and plan of every part, even during 
its growth. And as we look abroad over all the diversified 
forms of animated nature, the accuracy with which this 
force works in the prescribed mould of each is very won- 
derful. 

440. Life Sometimes Dormant.— While the 
vital force is in action there is constant change; but some- 
times it is dormant. A seed in its quiescent state has life 
in it, ready to be waked into action by the proper excitants, 
air. warmth, and moisture. Seeds that were found in the 

vations of Pompeii have shown that they retained 
their life during all this time, by shooting forth their 
they were exposed to these natural exci- 
tants of their growth. 

One of the moM interesting cases of this kind is related 
by Dr. Lindley. " I have now before me," be Bays, "three 



330 PHYSIOLOGY AXD ll\\xii-XE. 

plants of Raspberries, which have been raised in the gar- 
dens of the Horticultural Society, from seeds taken from 
the stomach of a man whose skeleton was found thirty 
feet below the surface of the earth, at the bottom of a 
burrow which was opened near Dorchester. He had been 
buried with some coin of the Emperor Hadrian, and it is 
probable, therefore, that the seeds were sixteen or seventeen 
hundred years old." 

A similar dormant condition of the vital force exists in a 
greater or less degree in the state of hibernation. So, also, 
in cold climates, life is throughout almost the whole vege- 
table world dormant during the period of winter, to wake 
to greater energy from the stimulating warmth of spring. 
In the human body, with the exception of some few very 
rare cases, life is always in an active state. Some portions, 
however, of the system are a part of the time dormant for 
the purpose of rest and repair. 

The brain and the muscles sleep ; but during their sleep 
life is busy in the formative vessels, repairing their energies, 
and we may say, their textures also, which have been wasted 
by their labor. It is a very wonderful attribute of the vital 
force that it can, as in the case of the hibernating warm- 
blooded animals, stop all its active operations, without dam- 
age to the machinery of life, and with such facility resign 
itself to a state of temporary inactivity. 

441. dlysterious Connection of Life with the 
Soul. — The most mysterious of all the circumstances in 
regard to the vital force is its connection in man with the 
immortal soul. The life and the soul are so intimately con- 
nected that some have considered them to be the same. 
But they are two distinct forces. They are in some measure 
indeed antagonistic to each other. For the soul, in using 
the machinery of the nerves and muscles, occasions a wear 
and tear of the structure, which it is the office of life with 
its numberless cell-laboratories to repair. 

The soul and the vital principle are both present in all 
parts of the system, but not in the same sense. The vital 
principle is seen equally at work every where. It has no great 



LIFE AXD DEATH. 331 

central organ from which it sends fortli its influence. But 
the soul is especially connected with the brain, and by means 
of the complicated nervous connections of this organ, it 
affects and is affected by all parts of the system. Its influ- 
ence is thus an all-pervading one. Every point of the 
living organization lias thus a sort of telegraphic communi- 
cation with the immaterial soul. 

But there is another view of this connection of the soul 
and the vital principle. The soul is developed in and with 
the living structure. It is not created by itself and put 
into the body as a tenant. Its powers are developed while 
the vital force develops the powers of the physical organiza- 
tion. The two processes go on together. Nay more, the 
development of the soul is in a measure dependent upon the 
development of the body. The vital force exerts a manifest 
influence upon the soul's growth. As it prepares the organs 
for the use of the soul — those organs by which it acquires 
knowledge from without, and thus procures the stimulus 
and even the material for its growth — whenever the vital 
force fails to construct these organs properly, the powers 
of the soul are not well developed. This we see exemplified 
in the idiot. 

In this intimate connection of the soul with life we find 
a great mystery. Life, a force belonging to mere matter, 
an endowment of it, or a compound of its endowments — life, 
that builds up all organized substances, the humblest and 
simplest vegetable growth as well as that most complex of 
all living structures, man — life, that so soon perishes in the 
noblest of its works that it is likened to the dissolving vapor 
— is made by the Creator an agent in developing an imma- 
terial principle or being, that is to survive the dissolution 
of the structure in which it is generated, and is to live for- 
ever. Strange that the immortal should be thus produced 
in the mortal — that the unchangeable and imperishable soul 
should be thus developed in such intimate connection with 
the changeable and perishable body. It is a mystery which 
we can not fathom. 

442. Natural Limits of Life Decay. — The vital 



332 PHYSIOLOGY AND HYGIENE. 

force, that is so busy in building and repairing so long as it 
lasts, has in all cases its natural limit; and in the case of the 
human system it seldom fully reaches this limit. The diver- 
sified, and complicated, and beautiful structures which it 
evolves, if saved from accident till the natural period of de- 
cline comes, lose their vigor and beauty, and at length die 
and are given up to the action of the common laws of chem- 
istry, which the vital force has so long resisted and con- 
trolled. The structures then decay, and the particles are 
dissipated, perhaps to be united again to other structures. 

443. Systemic and Molecular Death.— The 
death of the body is not ordinarily complete at the moment 
when what we term death occurs. Though as a whole, as a 
system of organs, the operations of life are at an end, yet there 
is some degree of life in some parts, and there may be in all 
parts of the body. The beard and nails even, may grow. 
Some of the organs may secrete their fluids — the liver its 
bile, and the stomach its gastric juice. Some of the properties 
of life, too manifestly, still remain. The irritability of the 
muscles, which is strictly a vital property, as it never belongs 
to common dead matter, still appears on the application of 
excitants. It was the contraction of the muscles in the leg 
of a dead frog on the accidental application of a stimulus, 
that led Galvani to his grand discovery. And it is through 
this vital property that the culprit who has been hung can 
be galvanized into apparent life. 

Death, then, may be said to be of two kinds — systemic, 
that is. the death of the body as a whole, a system of organs 
— and molecular, that is, the death of the individual mole- 
cules or particles which compose the body. Death can be 
said to be complete only when the laws of life have resigned 
their power over these molecules, and the laws of purely 
chemical action have taken their place. "When this change 
occurs, the process of decay, which is strictly a chemical 
process, begins. 

444. Death, beg inn in r j in the Heart and in 
the Lungs. — If a large quantity of blood be lost, so large 
as to result fatally, death in this case obviously begins in the 



LIFE AND DEATH. 333 

circulation. The heart not being supplied with the quantity 
of blood that usually flows through it, becomes more and 
more feeble in its action, till it at length ceases to beat. 
When a large aneurism bursts, it is the sudden drain from 
the circulation that destroys life. 

Any thing wmich to any great extent prevents the air 
from entering the lungs may cause death to begin in the 
respiratory system. This may be done by three classes of 
causes. 1st. Causes that act upon the large air-passages. 
Examples of this class of causes are strangling, smothering, 
drowning, &c. In croup the principal cause of death is 
the prevention of the free passage of air through the wind- 
pipe into the lungs. 

•-3d. Causes which act upon the walls of the chest. If a 
bank of earth fall upon a man, though it leave his head 
clear, so that the air-passages are unobstructed, he can not 
breathe, because his chest is held as if in a vise. A man 
came near dying from this cause who was having a cast 
taken of the upper part of his body. If the muscles of res- 
piration were to be paralyzed, death would ensue, just as it 
does when they are prevented from acting by other causes. 

3d. Causes acting upon the lungs. Disease may occasion 
an amount of obstruction in the very substance of the lungs 
sufficient to cause death. It does so by preventing the in- 
troduction of the air into the minute air-vessels, where the 
air revivifies the blood. The obstruction is just as effectual 
in this case as it is where it occurs in the large air-passages. 

44.~>. Death beginning in the Nervous Sys- 
te)n. — When death occurs from a blow upon the head as the 
immediate result of the shock, we have an example of death 
inning in the nervous system. Hut the cause may act 
upon this Bystem in some other quarter. A blow at the pit 
of the stomach, for example, may so shock the whole ner- 
vous system as to stop at once the operations of life. Some 
poisons, too, as opium, destroy life by their influence upon 
this system. Very extensive burns give a shock to the 
nerves from which they do not rally. The same can be 
said of other injuries when there is no recovery from the 



334 PHYSIOLOGY AND HYGIENE. 

first shock. Powerful medicines, improperly given in cases 
of disease disposed to prostration, may depress the nervous 
system to a point from which it may never revive. Cold 
destroys life mostly by the benumbing, paralyzing influence 
which it exerts upon the nerves. 

Though we thus classify the modes of death, in the great 
majority of cases death is a complex event, resulting from 
a concurrence of causes. It is so even when the disease is 
not of a complicated character. Take, for example, a case 
of pure uncomplicated consumption, in which all the organs 
but the lungs are in a healthy state to the end. The whole 
system becomes at length exhausted by the disease. If this 
exhaustion alone be the cause of death, then we may say 
that it is an example of death beginning in the nervous sys- 
tem. But if the obstruction in the lungs to the admission of 
air in the air-cells be the cause, it is a case of death begin- 
ning in the respiratory system. Generally in such cases 
death results from the two causes combined, and it is often 
difficult to determine which is the more prominent cause. 

446. Ttie Signs of Death. — The signs of death are 
so clear that there is, with very few exceptions, no mistake 
in regard to the occurrence of the event. The stories that 
are related about burying alive are most of them unfounded. 
The apprehensions created by them in the minds of some 
persons have led them to insist that no body ought to be 
committed to the grave till the most infallible sign of death, 
putrefaction, has appeared. We should wait for the appear- 
ance of this sign in all cases in which there is a shadow of 
doubt. But the cases are exceedingly rare in which we 
cannot determine the reality of death long before this sign 
shows itself. Our decision is not made up, it must be ob- 
served, merely from the signs of death. 

All the circumstances of the case are taken into view — 
the disease, its progress, its symptoms, and the events of the 
last hours of the patient. With this evidence before us, 
we absolutely know, in all ordinary cases, that death has 
occurred when the respiration and the circulation have 
ceased. And in the exceedingly few cases in which there is 



LIFE AXD DEATH. 335 

any reason to doubt on that point, there is always some- 
thing which will attract the attention and excite the curi- 
osity of some one, unless there be stolid indifference and 
the most absolute lack of intelligence. 

In such cases there is always something strange — the cir- 
cumstances attending the cessation of the respiration and 
circulation are singular, and the signs of death are not 
complete and in their proper order of succession. When- 
ever there is for these reasons any doubt as to the reality 
of the apparent death, the strictest watch should be main- 
tained till the signs of commencing putrefaction appear. 
With this simple rule of prevention burying alive need 
never occur. 

The investigations of physiology, as you have seen, end 
with the death of the body. It can give us no light on the 
question as to what may be beyond this life. Although the 
physiologist studies the human structure not merely as an 
organization instinct with life, but also as the wonderful 
machinery through which a reasoning soul acts and is 
acted upon in this state of being, yet, as a physiologist, he 
knows not that the soul survives the death of the body. 

He knows not but that it is a mere endowment of matter, 
as life probably is, and so perishes in the hour of dissolution. 
He may indeed conjecture that the exalted faculties which 
are in this world susceptible of such high cultivation, in- 
stead of being destroyed with the body, are destined to still 
farther development in another state of existence. But 
what is mere conjecture to him as a Physiologist, is made 
fact to him as a Christian. The eye of his faith sees an 
immortal spirit rise from the dying body, and he realizes 
the truth of the sublime declaration, that death is swallowed 
up in victory. 



336 QUESTIONS. 



QUESTIONS. 



CHAPTEE I. 



1. In what respect are a crystal and a plant alike? How do they 
differ in the modes of their formation? What different offices do the 
organs in a plant perform ? What is meant when we call the plant 
an organized substance, and the crystal an unorganized substance? Do 
the organs in the plant act wholly on mechanical principles ? 

2. Or on chemical? What principles control the mechanical and 
the chemical ? What two classes are there of organized living beings? 
How do they differ as to the complex character of their organization ? 
Under what two grand divisions do you class all the substances of the 
material world ? How do plants and animals differ from minerals as 
to the parts of which they are composed ? 

3. What is assimilation? Explain it as it takes place: — First, in 
the plant, and secondly, in the animal. 

4z» How do organized and unorganized substances differ as to per- 
manency ? Point out the mode and the extent of the change that occurs 
in the organized. Why is there more change in animals than in 
plants? How can minerals be changed? Are they productive, as ani- 
mals and plants are? 

«5. Contrast organized and unorganized substances in regard to 
change in the phenomena that you see in the world around you. How 
do organized and unorganized substances differ as to regularity in 
form? 

6*. What does irregularity in the unorganized arise from? How 
does the law of regularity operate in organized substances ? In which 
is the regularity the most wonderful, the organized or the unorgan- 
ized, and why ? 

7. Grive the four reasons assigned : — First, as to change ; secondly, 
as to variety of form ; thirdly, as to its continuance from age to age ; 
and fourthly, as to its preservation in the midst of a certain range of 
irregularity. Exemplify the last point by reference to the human 
countenance. How is the law of regularity exemplified in the two 
halves of the body ? Mention some organs which are destitute of this 
symmetry ; mention also some animals that do not exhibit it. What 



QUESTIONS. 337 

is the distinction between organized and unorganized substances as to 
limit of size ? 

$. How do organized and unorganized substances differ as to their 
structure? How do they differ as to the number of elements of which 
they are composed ? What are the four principal elements of organ- 
ize i bodies '? Which one of these is solid? In what form are the other 
three ? How many elementary substances are there in the material 
world? How many of these are found in plants and animals? 



CHAPTER II. 

f). Point out the difference between the plant and the animal as to 
k'Coniotiou. How does this difference make it necessary that tbe ani- 
mal should have a stomach ? 

10. Trace the analogy between the stomach in the animal and the 
roots iu the plant. What is the difference between most animals and 
plants as to central organs? What is their difference as to the effect 
of mutilation upon them V What is the distinction between animals 
and vegetables as to sensation and spontaneous motion ? Have all ani- 
mals consciousness and thought ? Name some exceptions to the dis- 
tinction as to locomotion. What is the difference between the mo- 
tions of such plants as the sensitive-plant and catch-fly. and those of 
animals ? 

11. Make the comparison in relation to the hydra, which describe. 
What part of the structure of animals is peculiar to them. Has this 
structure ever been discovered in any plant ? Why ought we to be 
able to discover it in the sensitive-plant and catch-fly, if it were the 

of their motions ? 

J 'J. Is tin- nervous system necessary to the carrying on of nutrition? 
What are the functions of organic life? What of animal life ? What is 
the order of action in the nervous system ? In what respect is this 
order not observed in some cases ? 

13, What is tin- distinction between animals and plants as to their 
chemical composition *.' In which is carbon the characteristic element, 
and in which is it nitrogen ? From what organs in animals is carbon 
thrown off? In what organs in plants is it absorbed ! 



CHAPTER III. 

13, How is man commonly classed in the animal kingdom? On 
what ground can the classification be claimed t<» 1><* rorr» - this 

nfication recognize at all the essentia] distinctions between man 
and other animala 
10 



338 QUESTIONS. 

14. What are those distinctions ? What bearing has man's immor- 
tality on this subject ? Is the difference between man and other ani- 
mals like that which we see between different animals ? 

!♦>. Is it a mere difference of degree? What notice should the 
naturalist take of the difference ? What is the distinction made in the 
common classification between man and such animals as apes and 
monkeys ? Can these animals be properly said to have four hands ? 
How do the hands which they are said to have resemble the hand of 
man, and how do they differ from it ? 

16. State some particulars in which the structure of man differs 
from that of the inferior animals. 

17 '. What relation have the peculiarities of man's organization to 
his mental peculiarities ? Why is it important that the essential dis- 
tinctions between man and animals should be prominently taught? 



CHAPTER IV. 

17* Of what two parts is bone composed? What are the propor- 
tions of these parts in childhood — in adult age — and in old age? How 
can you obtain these parts separate from each other ? 

IS, What is the animal part of bone? What relation does this 
sustain to the mineral part? What is the arrangement of the two 
parts of bone in the very young child ? What is true of the skeleton 
of many fishes? Of what are cartilages constituted? What two dif- 
ferent purposes do the bones fulfil ? 

10, In what two forms is bony substance deposited? How are 
these arranged in the flat bones ? How in the long ? How are both 
lightness and strength secured in a long bone — first, in the body of the 
bone, and then in its ends ? 

20. Why are the ends not made like the shaft ? What is the mar- 
row of the bone ? How is a bone nourished ? What is the periosteum ? 
Do arteries enter the solid substance of the bone? Describe the man- 
ner in which circulation is carried on in every point, as shown by the 
microscope. What fluid circulates in the minute channels in bone, 
shown to us by the microscope ? 

21. What is said of the sensibility of bone? 

22. Give a general description of the skeleton, noticing the variety 
of shape in the bones, and the purposes which they answer. How 
many bones are there in the head ? How many of these belong to the 
face ? How many to the cranium ? Describe the latter, as represented 
in Fig. 6. 

25. Why is the box (as the cranium may be called) holding the 
brain, composed of so many bones ? 

26. Describe the structure of the principal bones of the cranium 






QUESTIONS. 339 

What is the difference between the joinings of the outer and those of 
the inner tables of these bones? What is the reason of this differ- 
ence ? 

2 7. How are the principles seen in the construction of domes illus- 
trated in the cranium ? Of what bones is the dome of the cranium 
made up ? Describe the different ways in which strength is secured 
around the base of this dome. 

2&. Describe especially the arrangement between the parietal and 
temporal bones. When violence is inflicted upon the head, what is 
the direct rause of the injurious effects felt by the brain? On what 
principle do the guards of the brain defend against this cause of in- 
jury? 

29. Mention now in their order the different textures through 
which the vibration of a blow must pass before it reaches the brain, 
pointing out their agency in lessening the vibration. What arrange- 
ment is there of the lower part of the frontal bone as a special guard 
against injury at that point ? 

30. How is the side of the head, so peculiarly exposed to violence, 
especially guarded ? What other organs, beside the brain, are pro- 
tected by the cranium? Describe the arrangement of some of the 
bones of the face. 

31. Describe the cavities of the nostrils, and the sinuses connected 
with them. What is the object of the great extent of surface in these 
cavities? Describe the lower jaw. 

32. How many distinct structures are there in the teeth ? What 
is their arrangement ? How does a tooth differ from a bone ? 

33. What is the reason for this difference ? What is the necessity 
for having a second set of teeth ? Describe the hyoid bone, its posi- 
tion, and its connections. 

34. Mention other bones which, like this, are not directly con- 
nected with the bones of the skeleton. Of how many bones is the 
spinal column composed? Acting as the great pillar of the body, what 
does it support ? What is the pedestal on which it stands, and in what 
manner is this pedestal made firm ? While this column is thus firm, 
it needs to be flexible — how is this accomplished? Notice its differ- 
ent degrees of flexibility in different portions of it. Why is there so 
little motion in that portion that supports the framework of the 
chest ■; 

35. Besides serving as a firm pillar and a flexible chain, what other 
purpose does the spinal column fulfil \ Describe a vertebra. 

3(>. By what arc the vertebra? bound together 1 Describe the canal 
in this column for the spinal marrow. What is the arrangement for 
the n'-rvf-s that pass from it ? Bow an- the cartilages arranged ? 

37. What two purposes do they Subserve ? What is there in tin; 

shape of the spinal column that uard against shocks to 



340 QUESTIONS. 

the brain ? What are now the three objects secured in the structure 
of the spine ? 

38. Describe the contrivance at the top of it, as represented in 
Figs. 14, 15 and 16. Compare this with the mounting of a telescope. 
What is the difference in the two cases ? 

39. By what arrangement is the freeness of motion in the neck of 
birds made consistent with the security of the spinal marrow ? 

40. What is there peculiar in the spinal column of quadrupeds ? 
What is the paxy-waxy ? How are the vertebrae of fishes constructed 
and arranged ? 

4 1 . How is the great flexibility of the spine in reptiles secured ? 
How in the neck of the giraffe ? 

42. Describe the arrangement of the breast-bone, the collar-bone, 
and the shoulder-blades. What is the use of the collar-bone, and what 
are its variations in different animals ? How does the shoulder-blade 
differ from all other bones in the body ? 

44. Why is the socket of the shoulder-joint so shallow? Describe 
the arrangement of the radius and ulna, and the manner in which 
such free and varied motion is given to the arm. Describe the three 
parts of the hand ? 

45. Describe the ligaments that bind the bones of the hand to- 
gether. 

46. What is the principal object aimed at in the construction of the 
lower extremity ? What in the upper? Describe the thigh-bone. 

47 • What is the patella? What purposes does it answer ? What 
part of the foot is formed by the tarsus ? What part by the metatar- 
sus? How many bones are there in the toes? How many in the 
whole foot ? What object is secured by haVing so many bones in the 
foot ? Why is the foot arched ? 

48. Describe its movement in walking. With what are the ends 
of the bones tipped, and why ? What is the arrangement of the mem- 
brane that lines the ends of the bones ? 

50. What contrivance is there in the knee-joint, and in the articu- 
lation of the lower jaw? 



CHAPTEK V. 

50. Give the summary in regard to the action of the muscles, and 
their nervous connections. 

51. What are the tendons? What is said of the relation they 
bear to the muscles — their shape — their mode of union with muscles 
and with bones — their strength — and their size ? 

52. How are the muscles and tendons arranged in reference to con- 



QUESTIONS, 341 

venience and beauty? Illustrate by the arm and the hand. Illustrate 
the application of the first kind of lever in the action of muscles. 

J/>. So also of the second kind. 

54. And of the third kind. Which kind is most frequently used in 
the body ? 

.>/>. What two different objects are aimed at in the application of 
these two levers? Illustrate by examples of the second kind of lever. 

<>6*. Illustrate the same by examples of the third kind. What is 
the difference between the motion of the forearm on the arm, and the 
motion of the lower jaw, in the application of the principles alluded to ? 

~> 7 . Show how quickness is secured at the sacrifice of power in the 
case of the biceps muscle, as illustrated in Fig. 33. Under what me- 
chanical disadvantage do most of the muscles act, as represented in 
Fig. 34. 

o9. Show by this figure how quickness of movement is gained in 
this case. Why is the muscle, the deltoid, whose action is represented 
in this diagram, so large? 

00. How is the mechanical disadvantage, which thus results from 
the oblique action of the muscles, in part obviated ? Illustrate by Figs. 
35 and 36. Describe the agency of the patella in this respect. 

01. To what extent is the pulley used in the arrangement of mus- 
cles ? Show the application of the pulley, as seen in the ankle. 

O 2 . Describe the pulley arrangement of the digastric muscle. What 
is the necessity for such an arrangement ? 

03* What other office does this muscle perform, besides drawing 
down the lower jaw, and how does it do it ? Describe the muscles that 
move the ball of the eye. 

04, What is said of the actions of opponent muscles? 

6\>. Give some examples of the tonic contraction of muscles. What 
is the cause of wry neck, and of squinting? Illustrate the compound 
action of muscles by Fig. 32. How does variation in the degree of the 
contraction of muscles affect the variety of motion? What organ 
peculiarly exemplifies variety in muscular action ? 

00* Give a general description of the muscles of the body as ex- 
hibited in Figs. 41 and 42. 

70. What other parts besides the bones are moved by muscles? 
How are the muscles arranged in reference to convenience and sym- 

: ;be a peculiar arrangement of tendons and muscles in 
the sole of the foot. Describe the arrangement of tendons represented 
in Fig. 43. 

71. Describe the operation of the toggle-joint. Give examples of 
the application of this operation in the action of muscles. 

7'i. How many muscles are there in the hand and arm 9 What 
id of the extent of the variety of their action? What is thernus- 
Illustiate the operation of it in various wa- 



342 QUESTIOXS. 



CHAPTER VI. 

74. By what alone are thought and feeling expressed? By what 
mode of muscular action are thought and feeling mostly communi- 
cated? What relation has writing to this mode of communication? 
Describe the muscles of the face with the action of each as exhibited 
in Fig. 45. 

? 6'. Describe the muscles about the mouth, as shown in Fig. 46. 

77. In what way is the expression of the face made the same in its 
two halves ? 

78. Explain the agency of various muscles — the frontal — thecorru- 
gator supercilii — the superbus. What is the action of the muscles in 
quiet sorrow ? 

70. Is there commonly any one muscle devoted to the expression 
of any one emotion or passion ? Does the same muscle often take a 
part in the expression of various emotions? What is their state in the 
expression of a calm pleasure ? Illustrate the agency of the muscles of 
the eyeball in expression. What is said of the action of the oblique 
muscles? Why is the intoxicated man apt to squint and see double? 
Why does he raise his eyebrows in the effort to keep his eyes open? 
What other parts besides the face are brought into action in the Ian 
guage of the muscles. 

80. What is said of the action of the rest of the body in expression ? 
What muscles of the body sympathize most with those of the face in 
expression? Give examples in illustration. Explain the expression 
of the countenance, as seen after death. 

CHAPTER VII. 

81* Give a summary of the processes of digestion. 

82. Of what substances is the body of a tooth composed, and how 
are they arranged? What are the different shapes of teeth, and for 
what different purposes are they fitted ? How do the teeth of carnivo- 
rous animals differ from those of the herbivorous? How does the 
motion of the lower jaw differ in the two classes? What is the shape 
of the teeth in the insectivorous ? What in the frugivorous? 

83. What is the peculiar arrangement of the enamel in the teeth 
of the herbivorous, and for what purpose ? What can be inferred 
about an animal from an examination of his teeth ? Why is man said 
to be an omnivorous animal ? 

84=. Why are his tearing teeth less in length and in power than 
those of carnivorous animals ? What has the common whale instead 
of teeth ? What is the purpose of the arrangement ? 



QUESTIONS. 343 

S3. What supplies the place of teeth in birds? What is the use of 
the saliva t Describe the sit uation and arrangement of the glands that 
supply this fluid. 

80* How much saliva is secreted by the salivary glands during a 
meal? Why is more saliva than usual needed when one is speaking? 
What effect does motion of the mouth have on the secretion? How 
are these salivary glands affected by tobacco-chewing? Explain the 
influence of sympathy in the secretion of saliva. What are the two 
kinds of fluid secreted by the salivary glands, and what is the purpose 
of each kind ? 

ST. Describe the various parts engaged in the act of swallowing, as 
represented in Figs. 54 and oo. 

88* Describe the arrangement of muscular fibres in the oesophagus. 

SO. What is the character of the gastric juice ? By what is it 
formed ? 

00. Describe the appearance of the mucous membrane of the stom- 
ach, as seen by l>r. Beaumont, in the case of Alexis St. Martin. To 
what is the amount of gustric juice proportioned? What is the effect 
of stimulating the stomach to too large a secretion of it from day to 
day? What is the nature of its action on the food? How is the ap- 
plication of it to all portions of the food secured? Describe the ar- 
rangement of the muscular fibres of the stomach, and the manner of 
their action. 

01. What is the chyme? What is the arrangement of the valve 
called the pylorus? When is the pylorus especially in action? If 
there be difficulty in digesting the food, what is the effect on the action 
of this valve? What is the true character of the process? 

O.'j. What is the consequence if fresh food be introduced into the 
stomach while the process is going on ? Why is the practice of eating 
between meals a bad one? Why does eating fast, do harm? What 
effect has great variety in food? How does exercise affect digestion? 
Relate the experiment with the two dogs, and state what it proves. 

04:. What shows that hunger does not arise from emptiness? 
What that it does not arise from the irritation of the gastric juice? 
What is the cause of hunger? What is the seat of the sensation? 
Upon what does the degree of hunger depend? What must be the 
state of the stomach to have this sensation exist? 

93. How do mental impressions sometimes destroy the sensation 
of hunger? What is the cause of thirst? When* is its seat ? De- 
scribe the arrangement of the digestive organs as seen in Fig. GO. 

0(>. What are the uses of the mesentery ? 

97. Where are the bile and the fluid secreted by the pancreas 
mingled with the chyme v 

OS. What is one of the offices which they execute? What is the 

chyle? What are the lacteals? What glands do they enter 1 After 



344 QUESTIONS. 

passing on from these glands, into what duct do they empty the chyle ? 
What is the size of this duct, and where does it pour its contents ? 

99. Describe the operation of the suction power at the mouth of 
the thoracic duct. What becomes of the chyle thus forced into the 
blood ? What is the general rule by which the variation in the diges- 
tive apparatus in different animals is governed? Exemplify by a com- 
parison between herbivorous and carnivorous animals. What is the 
length of the alimentary canal in the lion? What in the sheep? 
What in man ? In what animals is the stomach most complicated? 

100, Describe the apparatus of digestion in the sheep, and its suc- 
cessive processes. Which of the four cavities in the sheep's stomach is 
the real stomach? Into which cavity does fluid matter always go? 
What is the arrangement when the animal is suckling? 

102, Describe the digestive apparatus of birds as exemplified in 
the turkey. What circumstances govern the variation of the digestive 
organs in different animals ? What is true of the stomach in the lower 
orders of animals? What peculiarity is there in the Hydra in regard 
to its stomach ? 



CHAPTER VIII. 

105, What are the different parts of the apparatus of the circula- 
tion ? Describe the agency of each in circulating the blood. 

1O0. What relation does the heart bear to the rest of the circula- 
ting apparatus? What is the difference between the arteries and the 
veins in their structure ? What two reasons are there for this differ- 
ence? What is the pulse? How do the arteries and veins differ in 
the mode of their division ? 

107 < How does the venous system differ from the arterial in capa- 
city ? How in regard to rapidity of flow of the blood ? Describe the 
valves in the veins. 

108. W T hy are these valves needed? Why is it more dangerous 
to wound an artery than a vein? Give some examples, showing how 
on this account the 'arteries are seated more deeply than the veins. 
Where are the arteries superficially situated ? 

109. What is the proper way to stop bleeding from an artery ? 

110. What is an aneurism? When a ligature is tied around the 
artery above the aneurism in a limb, how is the limb to be supplied 
with blood ? What is the chief agent in the circulation of the blood ? 
How can you illustrate the contraction and the dilatation of the heart ? 

111. What phenomena show that the blood-vessels exert an active 
agency in circulating the blood ? How does the circulation through 
the liver show that the capillaries are active agents in circulating the 
blood? 



QUESTIONS. 345 

113. Why are the veins generally full of blood after death, while 
the arteries are nearly empty ? What is the origin of the term artery? 
Why do we not in common language speak of the blood as running in 
the arteries as well as in the veins 1 

114:. What is the color of the blood in the arteries? What color 
has it in the veins? AVhere is it changed from red to purple ? What 
other chancres besides that of color take place? What would be the 
consequence if the dark venous blood should be sent to the brain? 
Where is the change in the blood from purple to red effected ? How 
is the apparatus arranged so as to send the purple blood to the lungs 
to be changed ? Explain the diagram showing the plan of the two 
circulations ? 

115. What is the difference in the two circulations as to the color 
of the blood in the veins and the arteries? What is the difference 
between the change of the blood in the capillaries of the lungs and 
that which takes place in the capillaries of the general system ? 

110. Describe the parts of the right half of the heart as repre- 
sented in Fig. ?0. Describe the manner in which the auricle and 
ventricle, with the valves, act. Give the illustration as represented in 
Fig. 71. What is the difference in size and strength, between the 
auricle and ventricle ? What is the size of the heart ? 

IIS. Describe the arrangement of the valves of the aorta. Describe 
the special provision to prevent leaking in these valves. How are the 
walls of the heart supplied with blood ? 

120. Describe the valves between the auricles and the ventricles. 
Why are they regulated by muscles? Why are there no valves where 
the blood pours into the auricle from the venae cavae? Describe the 
parts of the heart as represented in Fig. 74. 

12 2. Describe the circulation as given in the map of the heart in 
Fig. 75. 

1 23* Describe the situation of the heart and its blood-vessels, as 
represented in Fig. 76. 

121. What is the difference between the two Bounds of the heart ? 
What is the cause of the first sound? What of the second V How is 

pulse produced? Explain the impulse of the heart against the 
chest. 

/?.">. Explain the plan of the pericardium. 

126. lias the heart any repose? Give some calculations as to the 
amount of work it does in a lifetime. 



( II A PTBB IX. 

127. What two objects are effected by the respiration \ Of what 
are the lungs com] Po what Is their spongy lightness owing? 



346 QUESTIONS. 

How minute are the air-cells or vesicles ? In what way is the change 
produced by the air in them upon the blood ? 

128. Describe the arrangement of the larynx, the trachea, the 
bronchi, and the lungs, as exhibited in Fig. 79. How are the heart and 
the lungs arranged in the chest ? 

129. What is the pleura ? Why are the lungs not fastened to the 
walls of the chest ? 

ISO. Describe the manner in which the air is made to enter the 
chest in breathing. Describe the framework of the chest, as repre- 
sented in Fig. 80. How are both lightness and strength secured in 
this structure? Why are the ribs joined to the breastbone by means 
of cartilages ? 

131. What is the chief connecting material of this framework? 
What is the diaphragm, and how is it arranged? 

1 32. How does the diaphragm act ? Describe inspiration and ex- 
piration as illustrated by Figs. 81 and 82. 

134. In what way do other muscles, besides the diaphragm, act 
in respiration ? Describe their arrangement and action, as represented 
in Fig. 83. 

135. What is the arrangement of the muscular fibres between the 
ribs, and their mode of action? In what directions are the ribs moved 
by the muscles in the neck and between the ribs? Do these muscles 
act much, if at all, in ordinary easy respiration ? Under what circum- 
stances do they act strongly ? If air were admitted to the outside of 
the lungs by openings in the walls of the chest, what would be the 
result ? 

130. How are the blood and the air kept from mingling in the 
lungs, while they are brought so near together that the air changes 
the blood ? What experiment shows that blood can be acted upon by 
air through pores? How important is the office of the air-cells? 
What provisions are made for securing to them sufficient room under 
all circumstances ? Illustrate by reference to the state of things in 
violent exercise. 

13 7 • If the expansion of the chest be restrained in any way, what 
influence is exerted upon the air-cells? In what two ways does violent 
exercise injure the lungs when the chest can not be well expanded ? 

138. What is said of the influence of compression of the chest in 
the production of disease in the female sex? What is said of the ex- 
tent to which compression of the chest is often carried? What is said 
of the gradual moulding of the chest by continued compression during 
its growth ? 

14=0. How is death produced in drowning ? How is water prevented 
from getting into the lungs in any quantity ? If arterial blood could be 
supplied to all the organs while the breathing is stopped, what would 
be the result ? What contrivance has the whale for this purpose ? 



QUESTIONS. 347 

14:1. What is the arrangement of the gills of a fish? By what 
experiment can yon prove that it is the air in the water that acts on 
the blood in the gills, and thus keeps the fish alive? Why can not 
the fish use air that is not mingled with water ? What provision in 
the land-crab enables him to live in air as weD as in water? Describe 
the arrangement of the gills in the lob-worm, and the larva of the 
Mayfly. 

ll'J. How are the respiratory organs arranged in insects? What 
is the effect of covering their stigmata with varnish ? For what two 
purposes is the apparatus of respiration largely developed in birds? 
What special arrangement is there for securing lightness? 

111. By what experiment can you show that carbonic acid is 
thrown off from the lungs? What are the components of the air, and 
what is their proportion? Which of these is essential to life? Why 
would it not be well to breathe pure oxygen alone ? Where has it 
been supposed till recently that the oxygen of the air unites with car- 
bon to make carbonic acid ? Where does this union take place ? 
What facts settle the last question? 

IKS. Does the change effected by the air upon the blood in the 
lungs take place to some extent, when blood drawn from a vein is ex- 
posed to air? What experiment illustrates the manner in which the 
air acts on the blood in the lungs? 

117* How much carbon is contained in the carbonic acid thrown 
off from the lungs in twenty- four hours ? What effect does this gas 
produce upon the health if ventilation be imperfect ? 

US. What becomes of the carbonic acid thrown off from the 
lungs of animals? How is the air replenished with oxygen? How is 
the equilibrium preserved in different climates? What effect has 
light upon the discharge of oxygen from the leaves of plants? 

IKK By what process is the heat of the body maintained ? Trace 
its analogy to ordinary combustion. What was formerly supposed in 
regard to the place of the production of animal heat? What objection 
was made to this su position? Where was it at length discovered 
that the heat is made ? 

ISO, What are the three sources of fuel for keeping up the animal 
heat? Why is so large a quantity of oily food eaten in cold climates ? 
How do cold and tropical climates differ in the provisions of nature in 
this respect 1 How is the use of fat in maintaining heat exemplified in 
hibernating animals? Whence comes the heat produced by exercise? 
Why is heat in different animals proportioned to their degree of ac- 
tiviT 

181. Contrast the warm and cold blooded animals in this respect? 

132, What is the ordinary temperature of the human body) 
What is essential to comfort as to temperature in man ? Detail ex- 
periments which show how high a degree of temperature can be borne. 



348 QUESTIONS. 

How are the evil effects of excessive heat in such cases chiefly pre- 
vented ? 

153. How much does the state of torpidity vary in different ani- 
mals ? On what does the degree to which a deprivation of air can be 
borne depend ? 

154. How far are the chemical changes described in this chapter 
dependent on nervous action ? 



CHAPTEE X. 

155. By what is the building and repairing of the body done? 
Have the vessels by which this is done, the power of selecting their 
material from the blood? Give examples of the co-operation of the 
formative vessels in their work. How is the concert of action in these 
vessels illustrated in the definite but various shapes of the structures 
which they make? 

150. Illustrate the agreement necessary between different neighbor- 
ing sets of formative vessels in the process of growth. Illustrate the 
wonderfulness of the concert of action in the formative vessels, when 
there is a change of action. How is this exemplified in certain animals, 
as the frog ? 

158. Describe the agreement of action seen in the successive 
changes that take place in the formation, discharge, and healing of an 
abscess. 

159. How many kinds of waste particles are there ? By what ab- 
sorbents are those particles taken up that can be used again ? 

100. What organs probably fit them to be used again as a part of 
the building material? Where is the lymph, which they compose, 
mingled with the blood? By what are the particles that are wholly 
useless absorbed ? By what organs are they excreted or thrown off 
from the body ? Do these various organs excrete different parts of this 
waste ? 

1G 1. Give some examples in which other functions besides excre- 
tion are performed by the same organ. What are the various func- 
tions of the skin ? Describe its structure to show how well it is fitted 
for these functions. 

102. How extensive is the tubing of the sweat-glands ? 

103. What is the difference between insensible and sensible per- 
spiration? What are the sebaceous glands? What purpose do they 
serve? Where are they most abundant? Upon what does the 
rapidity of the change constantly going on in the body chiefly depend ? 
Which has the most influence on this change, mental or bodily 
labor? 

104:. Illustrate the influence of activity on this change by a com- 



QUESTIONS, 3-49 

parison between the frog and the canary bird. Illustrate the same 
influence by a comparison her ween different parts of the body. 

163. What is said of the mingling of life and death in the changes 
of the particles ? 



CHAPTEB XI. 

163.. By what are all the minute operations of the system per- 
formed? How do the cells differ from the cells in the cellular 
tissue V What do these cells contain ? What is to be said of their form ? 

166* Describe them a^ seen in the blood. Of what are the solid 
parts of the body composed 1 

167* How do the cells appear as seen in the Hydra? Upon what 
does the character of many of the textures of the body depend t What 
is the chief difference between the various glands of the body? Upon 
what do the colors of various parts depend ? Illustrate the selecting 
power of the cells. 

168. What is said of :he changes that take place in the contents 
of the cells ? How many kinds of ceils are there in the blood V What 
gives the red color to the blood? What are two of the offices of the 
colored cells? 

J (if P. How does their amount vary in different auimals, and in 
different individuals of the human race? Describe by the figure the 
manner in which absorption is performed on the surface of the mucous 
membrane in the bowels. 

1 70. Describe in like manner secretion by Fig. 102. 

171. How many fbriMa are there in a muscular fibre? What is 
each one of these fibrillar % What takes place in them when the mus- 
cle contracts? What is the cause then of the swelling out of a 
muscle when it acts? How minute are the cells in muse! 

17'*. What solid animal deposits are made by cells? Describe the 
arrangement in the enamel of the teeth. 

/ 7 •*• ( >f what are the nerves composed ? What has been found in 

abinations between the tubuli of the nerves 1 Bow axe 

tubuli made from cells? What is the extent of the agency of 

In the formation of every animal what precedes the appear- 

of any d 

/ 74* Describe r _ iment of the contents of an 1 . 

/7/>. Describe 1 sion of pi thai take place in the 

yolk preparatory to the formation <»f the l»ird. 

/;<>'. From what material are all the parts of the bird made? 

<>n between organised and unorganized 
is made between gravitation and cell- 

Compare tli.; exhibition of the - power In the minute 



350 QUESTIONS. 

and in the large operations of nature. What comparison can you 
make between the beauty of nature as seen by the naked eye, and its 
inner beauty revealed by the microscope ? 



CHAPTEE XII. 

178. How far are the functions of nutrition alike in animals and 
plants ? 

179. Through what system are the uses for which the body is con- 
structed secured ? Why are the functions that are performed through 
the nervous system, called functions of animal life ? Why are they 
also called functions of relation ? Through what intermediate instru- 
ment does this system perform its functions ? 

180. How does this system vary in complication in different ani- 
mals? How much is learned through the nerves and their subordi- 
nate organs, the organs of the senses ? What are the three parts into 
which the nervous system may be divided ? 

181. What three things are necessary to sensation ? Illustrate the 
necessity of each. What three things are necessary to voluntary mo- 
tion ? Describe the arrangement of the parts of the nervous system as 
represented in Fig. 110. 

183 • Describe the arrangement and structure of the brain as rep- 
resented in Fig. 111. 

184. What part of the nervous system is most immediately essen- 
tial to the continuance of life? And why? Illustrate by facts. What 
are the con vol utions of the brain ? 

185. Describe the membranes of the brain — the pia mater — the 
dura mater — the arachnoid. What is the arrangement of the gray and 
the white substance ? Does the arrangement of the convolutions favor 
the idea of the phrenologist ? Of what is the white substance of the 
brain composed ? What function is performed by it ? 

187. What tubuli transmit impressions from the brain? What 
transmit to it ? What is said of the size of the tubuli? What is the 
function of the gray substance ? In proportion to what does its amount 
vary in different animals ? Is there gray matter at the extremities of 
the nerves? With what are the cells in the gray substance mingled? 
What is said of the necessity of a supply of arterial blood to this sub- 
stance ? 

188. How does the arrangement of the gray and the white sub- 
stance differ in the brain, in the spinal marrow, and in the ganglions? 
What are ganglions ? What are plexuses ? Why is the gray matter 
so largely supplied with blood ? 

189. What is said of the manner in which the nerves terminate in 



QUESTIONS. 351 

the organs of the body ? Where are the Pacinian corpuscles mostly 
found ? Describe their structure. What do we know of their use ? 

1(H). What is there that is wonderful in the healing of a divided 
nerve ? What do the observations of M. Sequard show ? What fact 
was proved by the experiments of Dr. Haighton ? What nervous 
changes occur when a union takes place between parts that do not 
belong together? 

1W2. Do the same nerves answer for sensation and for motion? In 
what part of the body are nerves of different kinds kept separate ? 
How is it in all other parts ? What is the arrangement of the nerves 
that branch out from the spinal marrow ? What two purposes do the 
two roots of each nerve serve? How is this ascertained? 

193, Are there different nerves for different kinds of sensation ? 
How is it in the eye ? How in the nose? What i3 a nerve of common 
sensation ? What is a nerve of special sensation ? Is each nerve fitted 
for its own peculiar office ? Illustrate by reference to the nerves of the 
eye. Notice particularly the effects produced, if the nerve of common 
sensation in the eye be paralyzed. 

IfP-JL. Why are different parts of the body endowed with different 
degrees of sensibility ? What organ is more sensitive than any other ? 
How much sensibility have the muscles? How much have the bones? 
What fact is related to show the use of the sensibility of the skin in 
preventing injury? What change takes place in the sensibility of in- 
ternal parts when they become inflamed? W T hat benevolent purpose 
is there in this ? 

7f><>. Does a nerve, as a matter of course, have sensibility? What 
is true of the brain in relation to sensibility ? What of the heart ? Is 
the heart well endowed with nerves ? With what nerves is it en- 
dowed ? What is said of the nerves of motion in the face ? What are 
the appearances when the nerve of expression in the face is paralyzed? 
Why is this nerve called the respiratory nerve of the face? How are 
the motions of expression in the face connected with the motions of 
respiration? Describe the results when this connection is broken by a 
paralysis of the respiratory nerve of the face. 

ltt 7. How many different nerves are devoted to the eye? What 
are their different offices ? Of nerves going to the same part may one 
be palsied while another is not ? Give some illustrations. Give the 
case related by Sir ('. Hell. 

1US, Are the nerves of different kinds all alike in their structure 
and composition ? Why run not th(? impression producing sensation 
be transmitted by the same nerve with the impression producing 
motion? In what direction is nervous action in sensation? In what 
direction is voluntary motion? 

JfPfK Does voluntary motion occur sometimes in consequence of 
sensation, and somethne> not I Illustrate this. Give the resemblance 



352 QUESTIONS. 

of the nervous system to a telegraphic apparatus. What is true of 
motion caused by mental emotions? Give some examples of muscles 
that are wholly involuntary, and of muscles that are partially so. 

200. What is the difference between an excitor and a motor nerve? 
Illustrate by reference to the respiration — and the action of the muscular 
coat of the stomach. Why is the action of these two classes of nerves 
called a reflex action ? Do we know what is transmitted through the 
trunk of a nerve ? Does reflex action ordinarily occur without posi- 
tive sensation? Under what circum stances is sensation connected with 
it ? Illustrate by reference to the action of the respiratory muscles. 

201. State the two separate functions of the spinal marrow. By 
what arrangement are they performed ? Illustrate the modes of effect- 
ing sensation — motion — and reflex action. 

202. How does the brain differ from the spinal marrow as to inter- 
vals of rest? Illustrate the continuous action of the spinal marrow, as 
seen in the operations that go on in the system when the brain is 
asleep, or is torpid with disease. Besides these operations, mention 
some of the motions that can be excited through the agency of the 
spinal marrow independent of the brain. Cite some of the facts to 
show that voluntary muscles act involuntarily more often than is 
commonly supposed. 

203. Explain the involuntary action of muscles in walking and 
other like acts. What was formerly supposed in relation to the im- 
portance of the brain as a central organ of the nervous system ? How 
do we know that the brain is not directly essential to the maintenance 
of life? 

204:. What are the functions most essential to life? Upon what 
part of the spinal marrow do these depend ? Illustrate the extent to 
which the different parts of the spinal marrow are independent of each 
other. Is there any sensation independent of the brain ? 

2 OS. Why is the system of nerves, of which I have treated in this 
chapter, called the cerebrospinal system? What other system is 
there ? What are its purposes ? • 



CHAPTER XIII. 

205- What principles apply to the construction of the apparatus 
of the voice ? 

200. Into what two kinds are wind-instruments divided? Explain 
the manner in which the variation of note is produced in those of the 
first kind, by reference to the flute and the trombone. 

207 • Illustrate the same point in the operation of the flute-stop of 
the organ. What influence does the width of the vibrating column of 



QUESTIONS. 353 

air have upon the note? How is the note varied in those wind-instru- 
ments in which the length of the column of air can not be altered? 
What are some of the wind-instruments of the second class? How is 
the sound produced in these? How is the note varied? Illustrate by 
reference to the ived-stops of the organ. How are the various notes 
produced in the clarionet ? 

208* Trace the analogy, in the application of the principles of 
musical sounds, between the vibrating column of air, the reed, and tin 4 
strings in such instruments as the piano and violin. Explain the re- 
lation of the tube of the reed-instrument to the reed. 

2 Of), What is the trachea, and of what is it composed? What is 
the larynx ? 

210, Describe the parts of the larynx as represented in Fig. 122. 
Describe particularly the arrangement of the arytenoid cartilages and 
the vocal ligaments, as represented in Figs. 123 and 124. 

'211, Describe, by means of Fig. 12o, the manner in which the 
different notes of the voice are produced. 

"212. How do we know that the lower ligaments arc the true vocal 
chords Y Apply now the principles regulating the variation of note in 
common musical instruments to the vocal apparatus. Give Magen- 
die's experiment. 

21f*>. What is the tube of the vocal apparatus, which answers to 
the tube of a reed-instrument? How many outlets has it? From 
which does the voice generally issue? How is it in humming? What 
influence do the cavities of the nose have on the voice ? 

211, In what two ways is the size of the vibrating column of air 
in the tube of the vocal instrument varied ? What influence docs this 
tube have on the character of the voice ? How would the voice sound 
if it should come directly from the larynx, instead of passing through 
the tube attached to it ? 

21i>, What is said of the variety and precision of the action of the 
les in the modulation and articulation of the voice? How much 
do the ligaments vary in length in producing all the variety of notes 
of which the voice is capable? Give the calculation in regard to the 
minutenesa of the muscular action in passing from one note to another. 
What is said of skill in managing the muscles of the chest in speaking 
and ringing 1 Give the illustration of the bag-pipe. 

216+ What is one of the chief causes of " throat disease" in public 

speakers? What circumstances tend to produce this disease? In the 

articulation of how many letters is the tongue the chief agent? State 

&Cts to show that the tongue is not so ess< ntial to the powei of 

in commonly supposed. 

2 17. What letters an- chiefly formed by the teeth ? What is lisp- 

What letters arc chiefly formed by the lips? Why do children 

use labials so early and so freely I Of what are there terms of endear- 



354 QUESTIONS. 

ment composed in most languages ? Illustrate the agency of the nasal 
cavities in articulation. 

2 IS. Explain the difficulty called speaking through the nose. 
What is said of articulation in whispering? How is the variation of 
note in whispering caused ? Mention some of the attempts that have 
been made to imitate the articulation of the voice by mechanism. 



CHAPTEE XIV. 

219. How is sound produced? When is sound musical, and when 
discordant? What is said of the transmission of sound? What of its 
reflection ? 

220. Illustrate the influence of the reflection of sound in accumu- 
lating it. 

221. What is true of the facility of the transmission of sound 
through solids and fluids as compared with air? Illustrate it by facts. 
How is the fact that sonorous vibration does not readily pass from one 
medium to another, illustrated? Upon what does the degree to which 
the vibration is lessened in passing from one substance to another, 
depend? 

222. In what cases is the intervention of a membrane of essential 
service, and why ? Give a general description of the process of hear- 
ing. Describe the apparatus of hearing, as represented in Fig. 132. 

223. What is the object of the external ear ? What is the use of 
its ridges and prominences ? What is said of the external ear of ani- 
mals in comparison with man ? 

224:. Describe the tube of the ear. By what two means is it 
guarded against intruders ? Describe the drum of the ear and the 
little bones. What is the arrangement of these bones? What are 
their connections, and how do their muscles act upon them? 

225. How does the cavity of the tympanum communicate with the 
mouth, and why ? What part of the ear is the essential part of the ap~ 
paratus ? How much of the apparatus may be destroyed without 
entire loss of hearing ? 

220. Describe the parts of the labyrinth. Why is it better that 
the vibrating substance in the labyrinth be a fluid than a solid or a 
gaseous substance. 

227 • Describe now, step by step, the process of hearing. Is all our 
hearing done in this way ? 

228. What is said of the two ends of the apparatus of hearing ? 



QUESTIONS. 355 



CHAPTER XV. 

22 S. Into what two parts may the process of seeing be divided? 
What principles govern the construction of the mechanical part of the 
apparatus 1 What is the object of its arrangements? How is the 
second part of the process executed ? How does the transmission of 
light resemble that of sound ? 

229. What is the refraction of light? Illustrate by Fig. 136. How 
are the rays bent in relation to a perpendicular when they pass from a 
denser into a rarer medium ? How, when they pass from a rarer into 
a denser ? 

230. How are the rays refracted when they pass through a medi- 
um which has a concave surface? 

231m How many coats has the eye? Describe the arrangement of 
the parts of the eye, as represented in Fig. 130. What is the use of 
the sclerotic coat ? How is the cornea fitted into it ? 

232. What is the color of the choroid coat, and to what is it owing? 
Of what is the retina chiefly composed? What are the three humors 
of the eye ? Describe the chamber in which the aqueous humor is 
What is the consistence of the crystalline humor or lens ? Describe 
the vitreous humor. Why is it called vitreous ? Describe the various 
parts as they are more minutely delineated in Fig. 140. How is the 
aqueous humor formed ? How is it continually changed ? 

233. Describe the membrane called the conjunctiva. What are 
the ciliary processes ? Describe their arrangement. What is their use ? 

23-L* How are images of objects formed upon the retina? How 
can the fact that such images are formed, be proved? 

235. Why are these images inverted ? On what does the color of 
the iris depend V What is the principal office of the iris ? By what 
arrangement of its muscular fibres are its motions effected ? What is 
the office of the crystalline lens ? What is its shape ? Its structure? 

23d. What two purposes does the choroid coat serve? What is 
the state of the choroid coat in the albino? What gives the bright 
red or pinky hue to the iris in his rase? How does the color of the 
choroid coat vary in different animals? What is the character of the 
retina, and its office ? Trace the analogy between the optic nerve and 
the other nerves of sense 1 What resemblance is there to the nerve of 
touch in its termination? 

237. What is the defect in the operation of optical instruments, 
calle 1 spherical aberration, and how is it obviated in the eye? 

23 S. What is the difficulty in the operation of a common lens, 
called chromatic aberration? How in the eve? Contrast the eye with 

the telescope in regard to the facility with which the eye accommo- 



356 QUESTIONS. 

dates itself to objects at different distances. In what two ways is this 
accommodation effected ? 

239. By what defects in the structure of the eye in the near- 
sighted is this power of adjustment counteracted ? How is this diffi- 
culty obviated? What is the difficulty in the far-sighted? How is it 
obviated ? 

24:0. What is necessary to single vision in regard to the two 
images formed in the two eyes ? When are the two images in the 
eyes alike. 

24:1. In what cases are they unlike? Relate the experiment given 
in explanation. How is it that in such a case, while there are two 
images, and therefore two impressions sent along the two optic nerves, 
yet the impression on the mind is single ? Explain Professor Wheat- 
stone's stereoscope. 

242. What is the visual angle f Can we get a correct idea of mag- 
nitude by the visual angle alone ? Illustrate by the Figure. 

243. What circumstance must be known in regard to an object, in 
order to have our estimate by the visual angle correct? 

244. Illustrate the manner in which we get ideas of the magnitude 
of objects by comparison. Show how we sometimes are made aware 
of our dependence on this sort of evidence. Explain the use of the 
muscular sense in acquiring an idea of the size and distance of objects. 
Do all the images formed on the retina transmit impressions to the 
mind ? Illustrate in reference to ordinary vision by an experiment. 

245. What is the " Blind Spot " ? 

24(>. How is the eye situated so as to protect against injury ? How 
does the cushion of fat on which it rests serve to protect it ? In what two 
ways does the muscle that closes the eyelids serve as a protection to 
the eye. How is it protected by the eyelashes? How by the eye- 
brows? How are the eyelids constructed in reference to the protec- 
tion of the eye ? 

247 • How do the tears serve as a protection ? Why do fishes have 
no tear-apparatus ? Describe the arrangement of the tear-apparatus. 

248. Why do the tears overflow the edges of the eyelids when 
they are abundant ? What arrangement of glands is there on the eye- 
lids ? What two purposes does the oily substance formed by them 
serve? How are the tears conducted into the mouth of the ducts 
when the eyelids are closed ? Describe the nictitating membrane in the 
eyes of birds. 



CHAPTEE XVI. 



249. From what two sources are the rules of hygiene to be learn- 
ed? How far is a knowledge of physiology necessary to a proper 
understanding of these rules ? 



QUESTIONS. 357 

250. What division of topics should be made in the subject of 
hygiene ? 

251. What points in the hygiene of digestion have been before 
noticed '? What is said in regard to the amount of food needed by the 
body? How can we know what this amount is? What errors are 
committed in regard to quantity of food ? 

252. From what causes is too little food sometimes taken ? What 
3s said of the intervals between our meals? What is said of eating 
regularly ? 

253. What of the different kinds of food? What of fruits? 
What influence has the mind on digestion ? 

254. What is the general statement in regard to tlie hygiene of 
respiration ? In what two ways is the free access of the air to the 
lungs interfered with ? What general rule is given as to dress in 
regard to the chest ? In what ways does compression of the chest 
occasion disease ? 

255. Why ordinarily is the influence of defective aeration (or air- 
ing) of the blood not appreciated ? What is the office of the organs 
of the circulation? Is the action of these organs ever violent and 
tumultuous ? 

250. What influence has muscular exercise on the development of 
the organs of the body? How is it a preservative against disease? 
What is said of violent exercise ? 

257 . What is the change going on continually in all parts of the 
body ? What two conditions are necessary to the proper performance 
of this change? What is said of the discharge of waste matter from 
the system? What organs effect this discharge? 

25S. How much matter is discharged from the skin? How is the 
animal heat produced ? How does exercise increase it ? What influ- 
ence has the quality of the blood upon it ? 

25U. What is essential to a comfortable temperature of the body? 
When one is too much heated how is the extra heat disposed of? 
What is the object in covering the body with clothing and in sur- 
rounding it with heated air? What is said of cold as a cause of dis- 
: What ar<* our means of guarding against cold? 

2(>0. How should we regulate the' amount of clothing? What is 
said of guarding against cold when the body is in a state of rest V 
What is said of the weak suffering from exposure to cold". How 
should the shoes of delicate females be made? 

261. Tnder what eiicumstances docs cold act as a stimulant? 
What circumstances are nerv ssary to this result? What arc the con- 
ditions on which reaction depends? 

262, What rules should be observed in the use of cold bathing? 
What are the best times for using it v what occasions the wear and 
tear of the system : When is most of the repairing in the system done? 



358 QUESTIONS. 

263. What is said of the relation of exercise to health ? What 
effect has it on the muscles themselves ? What on the other textures ? 
How does it prevent deformity ? 

264. What are the two causes of the common deformity of the 
spine ? Explain their action. Why is this deformity found so much 
more often in females than in males ? 

265. How much influence has posture in producing it? What 
especially debilitates the muscles of the back in the female ? Illus- 
trate the necessity of having exercise varied — also of having it general. 

266. What is said of gymnastics and calisthenics? What is said 
of having the exercise habitual ? How does too much exercise do 
harm ? What is said of having the exercise agreeable ? 

267 '• What is said of the hygiene of the senses ? What is said of 
the necessity of seasons of rest for the brain ? What significant fact 
in regard to insanity shows this ? What is said of the conditions 
under which the mind can perform much labor without harm ? 

268. What is said of overworking the brain during its growth ? 
What of the manner in which the child's mind is ordinarily exercised? 
What two mental causes acting together injure the health and some- 
times produce insanity? 

269. What influence has the regulation of the passions on the 
health ? On what portions of the system do alcohol and tobacco 
chiefly act ? What is said of alcoholic stimulants ? 

270* Show how tobacco may act indirectly as a stimulant. What 
are its effects on the system ? To what class of persons is it especially 
injurious ? What is the evidence in regard to the influence of tea and 
coffee ? 

27 1. What is said of emanations from filth as producing disease? 
Give a summary of the chief causes of disease. Is disease commonly 
produced by any one of these causes alone ? 

272. What is said of our control over these causes? What other 
causes of disease are there ? To what extent do they act compared 
with those mentioned? How may we often escape their influence? 
What is said of the comparative value of preventive and curative 
measures ? Illustrate the prevalent error on this point by reference to 
consumption. From what does the common neglect of preventive 
measures arise, and how can this be obviated ? 



CHAPTEK XVII. 

273. What is said of the brain as the organ of the mind ? What 
facts show that motion and sensation are dependent on the brain ? 
How does it appear that the mind thinks only by means of the brain ? 
How is life continued when sensation, motion, and thought are stopped 



QUESTIONS. 359 

by compression of the brain ? How does the variation of the degree of 
compression vary the effect on the mental functions? 

**7<5* Of what is insanity always the result ? How do moral causes 
produce it? If the mind were separate from the body, could insanity 
be produced in it? Can the disease in the organization in insanity, be 
always discovered in an examination after death? Describe the situa- 
tion of the brain and its immediate connections. What is said of the 
face V 

270. Illustrate the rapidity of the communication between the 
mind and the different parts of the body. How does a child learn to 
use its muscles? 

'J 7 7* What is said of the amount of knowledge acquired by the 
child in the first year of his life? What is said of skill in the use of 
the muscles ? What is said of the training of the senses ? 

27S. Illustrate the fart that the senses and muscles arc mutual 
teachers in their training. How does the dependence of the muscles 
on the senses differ from that of the senses on the muscles? What 
fact illustrates the absolute dependence of the muscles on the senses? 
In the education of the muscles and the senses, what is, strictly speak- 
iug, educated or trained? Illustrate by reference to the idiot and the 
deaf-mute. Why does not the education of the muscles extend to 
those that are involuntary ? 

'*7f>. What difference is there in the different stages of the train- 
ing of the muscles in the degree of cognizance which the mind takes 
of their action? Illustrate by reference to learning to walk, to read 
and to sing. What part of the brain has an especial connection with 
the mind? What is the chief office of the cerebellum? Give the 
evid -nee from comparative anatomy on which this point is settled? 

281. What experiments lead to the same conclusion? What is 
said <>f the comparative amounts of the white and the gray substance in 
the brain ? 

•-^.S'?. In what portion of the brain is the process of thinking carried 
r.n? What is the facial angU ? What is the difference in regard to 
this between the skull of the European and that of the African ? 
What between the skull of animals and that of man? What is the 
common measure of this angle in ancient statues of deities and heroes? 

283. What is Bald of the rule that the amount of intelligence, both 
in man and in animals, is proportioned to the amount of the cerebrum ? 

2 S'-/. What facts show that size is far from being the only measure 
of power in case of the brain 1 In studying the comparative physiology 

of the brain, what significant fnct do we find when we come to paSfl 
from the higher animals to man 1 Of what character is the mental 
difference between them and man? What is said of the definiteness 
of the distinction between man and animals? What note ought to be 
made of this distinction by the comparative physiologist? What arc 



360 QUESTIONS. 

the three sources of our knowledge in relation to the connection of the 
mind and the body? What is the consequence if we rely upon any 
one of these alone ? 

285. What is the alternative to which one is driven, if he confine 
himself to the evidence which physiology furnishes? What course 
is commonly pursued by those who take this narrow view of the sub- 
ject ? What is said of the distinction between organized and unor- 
ganized matter? What are the common suppositions in regard to the 
endowment of organized or living matter? What is said of those 
endowments of living matter that are connected with the nervous 
system ? 

286. What question now arises in relation to intelligence in its 
connection with matter ? What does physiology show us in regard to 
this connection ? Point out the deficiencies of its teaching in relation 
to the nature of this connection. What is the tendency of its pre- 
sumptive evidence? 

287 . Looking at the subject solely in the light of physiology, what 
would be the conclusion in regard to the dependence of mind on organ- 
ization, when we observe the origin and growth of a thinking animal? 
What bearing on this point has the fact, that the intellect grows with 
the brain and appears at last to perish with it? What fact in com- 
parative physiology is strongly adverse to materialism ? In which di- 
rection, however, on the whole, does the evidence from physiology, 
taken alone, preponderate? 

288. State the ground of the great need which the physiologist 
has of the evidence from other sources besides his physiology. 

280, What is the testimony of consciousness in relation to the 
independence of the soul in its action ? What in regard to its respon- 
sibility for its acts ? How far is this testimony acted upon by all, when 
physiological speculations are left out of view ? What does the evi- 
dence from consciousness show us in relation to the connection of the 
mind with the material organization? To what alternative does it 
drive us? 

290. How is this testimony of consciousness treated by the 
Bible? 

291. Illustrate our dependence on the Bible for the proof of the 
sours immortality ? How may the decrepancies in the evidence from 
physiology in regard to the connection of the mind and the body be 
cleared up? 

292. What is said of the character of the evidence drawn from con- 
sciousness and Revelation ? What is said of the presumptive evidence 
from physiology in comparison with it ? What is said of the present 
moral tendencies of physiological investigations ? 



QUESTIONS. 361 



CHAPTER XVIII. 

293. What was Lord Monboddo's idea of the development of man? 
What recent theory has an analogy to this ? What is true of man and 
animals in relation to instinct and reason? 

294=. Do we know what the nature of instinct is? Which can be 
understood best, the actions of instinct or those of reason ? Illustrate 
this point. What seems to produce the actions of instinct? What 
influence does the intelligence of the animal exert upon them ? What 
is said of the in variableness of the actions of instinct. 

295. Describe the nests of the Baya and the Tailor Bird. What is 
said of the perfection of the actions of instinct ? Why are the cells of 
the honeycomb made hexagonal ? Describe the arrangement of the 
ends of these cells. 

297. Give the fact stated in regard to the angle made by the sur- 
faces at their ends. How is the perfection of the actions of instinct 
seen in animals that live in communities? Describe the structure of a 
wasp's nest. 

29 S. Give the description of the habits of the beaver. 

300. In what respect may instinct be said to be blind? Illustrate 
by reference to animals that provide for a progeny which they are 
never to see. 

301. Why is it often difficult to distinguish between the results 
of reason and those of instinct ? What would be true of instinct if it 
were at all rational ? Under what circumstances is there perfection in 
the actions of instinct? Under what circumstances does it fail ? Con- 
trast instinct and reason in this respect. Give some illustrations of the 
characteristics of instinct alluded to. Give Mr. Broderip's account of 
the beaver. If the beaver in this case had been guided by reason, 
what would he have done ? 

302. How far is the care that animals take of their progeny gov- 
erned by a blind instinct ? What is said of the temporary character 
of parental affection in their case ? In what case is there no affection 
at all ? 

303. What degree of intelligence is shown in the power of imita- 
tion in animals? How do animals show that they reason ? How far 
did the beaver, whose story is given in § 409, reason? How does the 
character of the inferences made by animals differ from that of those 
made by man? illustrate by reference to Newton and his dog. 

304. Of what arc the inferences made by animals the results? 
When the proee>s<-< of thought in animals are extended and eompli- 

:. what is true of them? Illustrate by examples the extent to 
which mental association may be carried in the animal. 
300. Ho w do animals learn the relation of cause and effect? Illus- 
16 



362 QUESTIONS. 

trate by examples. How does this knowledge of cause and effect differ 
in man and in animals ? Is the mental difference between man and 
animals one of degree only ? 

307* What attribute constitutes the great superiority of the human 
mind? Show how this attribute is the origin of language in man. 
What is the character of the language of animals ? Why can not they 
have a language of arbitrary signs ? What is the source of man's be- 
lief in a Creator ? Illustrate this point. Is this belief implanted in the 
mind ? 

308. What two suppositions have been offered in relation to con- 
science ? What is said of the doubts which some entertain as to the 
existence of conscience? What is true of those cases in which animals 
seem to some to have a moral sense ? Illustrate the fact that in com- 
mon language we recognize the difference between man and animals as 
to the possession of a conscience. 

30i). Give a summary of the mental differences between man and 
animals. Give the gradations which we find in the nervous system as 
we trace the animal kingdom upward. 

CHAPTER XIX. 

310* Mention some of the contrasts which we find on looking over 
the human race. How many varieties of the race are commonly reck- 
oned? 

311* What are the characteristics of the Caucasian variety ? What 
are the characteristics of the Ethiopian varieties — the Mongolian — the 
American ? 

312. What are the characteristics of the Malay variety ? What is 
said of the extent to which the race maybe divided into varieties? 
What is said of the way in which national differences are produced? 
What is the opinion of most naturalists in regard to the production of 
the races? What is the doctrine of Professor Agassiz and others? 
State the grounds on which lie bases his doctrine. What is his opinion 
in regard to climatic and other influences ? What is his opinion of the 
history given in Genesis ? Are the different branches of the race in 
his view different species, or mere varieties? What is the distinction 
between a species and a variety ? 

315. Mention the influences included in the expression, climatic and 
other influences. What is said of the influence of climate ? What is 
the circumstance which has most influence in producing varieties in 
man and in animals ? What is included in the term domestication ? 
What is the precise question in regard to climatic and other influences? 

310. Mention some facts that show that climate has a great influ- 
ence on the color of the race. What influence do intellectual and 
moral causes exert upon the shape of the head ? 



QUESTIONS. 3G3 

317 * What is said of certain changes in form produced by causes 
the operation of which we do not understand? What are the three 
different types of form in the head stated by Dr. Pritchard, and by 
what causes are they -produced) State in regard to each: — the prog- 
nathous — the pyramidal — the oval. 

3 IS* Give some facts showing that these types are convertible into 
each other. What is said of the insensible gradations by which the 
varieties of the race pass into each other? 

319* What effect has the influence of domestication on both man 
and animals? What two objections are brought against the alleged 
competency of climatic and other influences to produce the varieties 
of the race? What great fact is a sufficient reply to these objections? 

320m Apply this fact in explanation of the production of the varie- 
ties of the human race. What is said of the analogy thus drawn be- 
tween man and animals, in comparison with that which Professor 
ssia has tried to establish? What consideration weakens his an- 
alogy v If the climatic and other influences appear to any one incom- 
petent to produce the varieties of the race, is he driven necessarily to 
admit its multiple origin ? 

321m What is said of the occasional introduction of new causes by 
the Creator? Upon what do our calculations upon the regularity of 
nature depend ? What is said of the change in the age of man effected 
at the time of the flood? 

322m What is said of the occasional appearance of new diseases? 
What is said of the convulsions which have evidently taken place in 
arth ? Does it make any difference to the argument, whether the 
results came directly from causes, or from a chain of causes? 

323m Apply the argument to the production of the varieties of the 
race. What is said of the objection to the argument, that it is suppos- 
ing a miraculous interposition? 

324* Is the supposition thus made needed? What is said of it in 
parison with the supposition of A;rissiz? On what principles is 
tli.- testimony of the Bible as t o the origin of the race to be interpreted I 
What are the main facts which it gives in relation to it 7 How is the 
truth of its testimony confirmed? Of what force is analogical and 
presumptive evidence in opposition to it Y Is any fear to he entertained 
in regard to bringing the Bible to thi bained lac- 



(HA PT E B XX. 

32&m " ..id .of the diversity in the manifestations of life? 

Bow is life always the same in relation to its origin'.' Remark on the 
wonderful variety of results worked out by the vital force beginning 
mple c •!!. 



3G4 QUESTIONS. 

320. How is life always essentially the same in its processes as well 
as in its origin ? Do we know what life is ? How does the vital force 
differ from such forces as light, heat, and electricity, in regard to its 
power of diffusion ? How in regard to self-generation ? How in regard 
to the variety of its effects ? 

327* Do we know whether life is one thing? What is said of the 
supposition that the principle of life resides chiefly in the blood? 
What are the relations that exist in living bodies between the laws 
of chemistry and mechanics and those of life ? Illustrate this point ? 

328. What is said of the materials of which the human body is 
composed, and of the degree of heat in which they are kept ? Show 
the difference in the operation of heat on dead and on living matter, 
as seen in the egg. 

329. How is the power of the vital force exhibited in the uniform- 
ity of the heat of the body ? What is said of the changes going on by 
the operation of the vital force? Remark on the dormant condition of 
this force in the case of seeds. 

330. Remark on the analogy between the hibernation of animals 
and the state of most of the vegetable world in winter. What portions 
of the human system are some of the time dormant, and why ? What 
is the most mysterious circumstance in regard to the vital force ? Show 
how the soul and the vital force are two distinct, and, in some measure, 
opposing forces. In what different senses are they both present every- 
where in the system ? 

331. What is said of the development of the soul in the body? 
What of the mystery of this connection ? What is said of the limit of 
the vital force ? Has the vital force a natural limit ? 

332. What is the distinction between systemic and molecular 
death ? How may death begin in the circulating system ? 

333. Give the three classes of causes by which death may begin in 
the respiratory system. Give examples of death beginning in the 
nervous system. 

334. Illustrate the fact that death is commonly a complex event. 
What is said of the signs of death ? What is said of the clearness of 
the evidence in all ordinary cases in regard to the fact of death ? 

335. In the very few cases in which there is any doubt, what 
course should be pursued ? What light can physiology give us in re- 
lation to what is beyond this life? What is said of the conjectures on 
this subject which its investigations may prompt ? 




GLOSSARY. 



Ab-do'tnen, (Latin abdere, to conceal.) The largest cavity of the 
body, containing the liver, stomach, intestines; etc. ; the belly. 

At>-duc'tor, (L. abducere, to lead away.) A muscle which moves 
certain parts, by separating them from the axis of the body. 

Absorbents, (L. ab y and sorbere, to suck up.) The vessels which 
take part in the process of absorption. 

Ab-soi'p'tion. The process of sucking up fluids by means of an ani- 
mal membrane. 

A-cc-tab' u-tum, (L. acetum, vinegar.) The socket for the bead 
of the thigh-bone ; an ancient vessel for holding vinegar. 

Ac' id, Ac'etie, (L. acetum, vinegar.) Relating to acetic acid. 
This is always composed of oxygen, hydrogen, and carbon, in the 
same proportion. 

Ac id, Lactic, (L. lac, milk.) The acid ingredient of sour milk ; 
the gastric juice also contains it. 

A-chil'les. A term applied to the tendon of two large muscles of 
the leg. 

A-cro'tni-on, (Gr. axpoc, akros, highest, and u/uor } omos, shoulder.) 
A process of the scapula that joins to the clavicle. 

Ad-duc'tov, (L. adducere, to lead to.) A muscle which draws one 
part of the body toward another. 

At -bu' men or Albumin, (L. albus, white.) An animal substance re- 
sembling white of egg. 

Al-bn'nii->tosc, (from albumen.) A soluble animal substance 
produced in the stomach by the digestion of the albuminoid sub- 
stances. 

^it-bit' ntin-oid substances. A class of proximate principles resem- 
bling albumen ; they may be derived from either the animal or 
v. ^etable kingdoms. 

Al'i-ment 9 (L. alere, to nourish.) That which affords nourishment ; 
food. 

At-i-mcnf 'fi-rif Cfl-nal, (from aliment.) The tube in which the 
food is digested, ojr prepared for reception Into the system. 

At ' ve-o-Uiv, ( L. aheolUit a socket.) Pertaining to the sockets of the 
teeth. 



366 GLOSSARY. 

An-OBS-thetr' ics, (Greek «r, an, without: aiodrioia, istliesia, feeling.) 
Those medicinal agents which prevent the feeling of pain, such as 
chloroform, laughing-gas, etc. 

A-)H(s'to-moK<', (Or. avu, ana, through, and nrnua, stoma, mouth.) 
The communication of arteries and veins with each other. 

A-nat'o-mij, (Or. ava, ana, through, and tout], tome, a cutting.) 
The description of the structure ot animals. The word anatomy 
properly signifies dissection. 

An-i-maV vuh> 9 (L. animal' culum, a small animal.) Applied to 
animals which can only be seen with the aid of the microscope. 
Animalculum (plural, animaicula) is used with the same meaning. 

A-ov'ta 9 (Gr. doprr), from ueipeiv. aeirdn, to lift, to be lifted up.) 
The largest artery of the body, and main trunk of all the arteries. 
It arises from the left ventricle of the heart. 

Ap-o-neu-ro' sis, (Gr. aito, ap>, from, and . i uron, a nerve.) 

The membranous expansions of muscles and tendons. The an- 
cients called every white tendon neurovo, a nerve. 

A'que-ons Humor, (L. aqua, water.) The watery colorless fluid 
occupying the space between the cornea and crystalline lens. 

A-rach'noid Mem'brane, (Gr. updxvn, arachne, a cobweb, and 
eiSog, lidos, like.) An extremely thin covering of the brain and 
spinal cord. It lies between the dura mat< r and the pia mater. 

Av'bor Yi'tue 9 (L. the tree of life.) A name given to the peculiar 
appearance presented by a section of the cerebellum. 

Ar'ter-t/, (Gr. d?jp, aer, air, and rqpeiv, terein, to contain.) A 
vessel by which blood is conveyed from the heart. It was sup- 
posed by the ancients to contain air ; hence the name. 

Ar-tic-u-la'tion , (L. articulare, to form a joint.) The more or less 
movable union of bones, etc. ; a joint. 

A-ryt-e'noid, (Gr. apvraiva, arutaina, a ewer, and eidoc, eidos, 
form.) The name of a cartilage of the larynx. 

As-phyx' i-a 9 (Gr. a, a, not, and u^uf/c, sphyxis, pulse.) Originally, 
want of pulse ; now used for suspended respiration, or apparent 
death. 

As-trag' a-lus 9 (Gr.) The name of a bone of the foot, One of the 
tarsal bones. 

As-sitn-i-lq,'tion 9 (L. ad, to, and similis, like.) The conversion of 
food into living tissue. 

Au-di'tion 9 (L. audire, to hear.) The act of hearing sounds. 

Au'di-to-ry Nerve. The special nerve of hearing. 

Au'ri-cle 9 (L. auris, the ear.) A cavity of the heart. 

Aoc-il'la, (L.) The arm-pit. 

A-ZOte' ' 9 (Gr. a, a, not, and <u?), zoe, life.) Nitrogen. One of the con- 
stituent elements of the atmosphere. So named because it will 
not sustain life. . 



GLOSSARY. 3G7 

Bel-la-don' na * (It. beautiful lady.) A vegetable narcotic poison. 

It lias the property of enlarging the pupil, and thus increasing 

the brilliancy of the eye. 
Bi-ats'j>id, (L. bis, two, and euspis, prominence.) The name of the 

fourth and fifth teeth on each side of the jaw. 
Bile, (L. Wis.) A yellow viscid fluid secreted by the liver. 
Broneh' % 3 (Gr. fipoyxoc, Wonkas, the windpipe.) The two great di- 
visions or branches of the trachea. 
Broncli' i-a! Tubes* The smaller branches of the trachea within 

the substance of the lungs, terminating in the air-cells. 
Bronch-i'tis, (from bronchia, and itis, an affix.) An inflammation 

of the larger bronchial tubes. 
Bur' sac Jlu-co'sa 9 (L. bursa, a purse, and mucosa, viscous.) Small 

sacs, containing a viscid fluid, situated about the joints, under 

tendons. 
Cal-ca-re'ou$, (L. calx, lime.) Containing lime. 
Co-nine* ', (L. cants, a dog.) Name given to the third tooth on each 

side of the jaw ; in the upper jaw it is also known as the eye-tooth. 
Cap' il-la-rt/, (L. captt'lus, a hair, capilla'ris, hair-like.) The name 

of the extremely minute blood-vessels connecting the veins. 
Car-bon'ic Ac-id, or Car'bon Diox-ide, (C0 2 .) The gas 

which is expired from the lungs. 
Car'di-ac, (Gr. napdia, kardia, the heart.) The upper orifice of the 

stomach near the heart ; hence its name. 
Car-nil/ O-rous, (L. ca'ro, flesh, and vora're, to devour.) Subsist- 
ing upon flesh. 
Ca-rotfid, (Gr. napoc, haras, lethargy.) The great arteries of the 

neck that convey blood to the heart. The ancients supposed 

drowsiness to be seated in these arteries. 
Ca'se-ine, (L. cdseus, cheese.) The albuminoid substance of milk ; 

it forms the basis of cheese. 
Car'ti-laf/e, (L. cartUago) Gristle. A smooth, elastic substance, 

softer than bone. 
Ca'va, (L.) Hollow. Vena cava. A name given to the two great 

veins of the body. 
Cer-e-bel'lum, (diminutive of cer'ebrum, the brain.) The little 

brain, situated beneath the cerebrum. 
Cc^e-bruin, (L.) The brain proper, occupying the entire upper 

portion of the skull. 
Cere-bro-Spi'nal. Relating to the brain and spine. 
Chvr f da-<B 9 (L-) A cord An assemblage of fibers. 
Clio'roid, (Gr. 7 ion, a membrane or covering.) The mid- 

tnnic or coat of the eyeball. 
Chyle, <<«r. Y'/''".-, chubs, juice.) The milk-like fluid formed in the 
Intestines by the digestion of fatty articles of food. 



368 GLOSSARY. 

Chyme 9 (Gr. x v l U0 C f chumos, juice.) A kind of grayish pulp formed 
from the food in the stomach. 

CWi-a 9 (pi. of cil'i-um, an eyelash.) Minute hair-like processes found 
upon the cells of the air-passages, and other parts that are habitu- 
ally moist. 

Cln-e-ri'tiou$ 9 (L. cinis, ashes.) Having the color of ashes. 

Civ-cu-la 'Hon 9 (L. circulare, to move in a circle.) The circuit or 
course of the blood through the blood-vessels. 

Clav'i-cle, (L. clamcula, from dams, a key.) The collar-bone ; so 
called from its resemblance in shape to an ancient key. 

Co-ag-ii-la'tion 9 (L. coagulere, to curdle.) Applied to the process 
by which the blood clots or solidifies. 

Coch'le-a 9 (Gr. /co^Aw, kochlo, to twist ; or L. cochlea, a screw.) A 
cavity of the ear resembling in form a snail shell. 

Co f lon 9 (Gr.) A portion of the large intestine. 

Col-um'na 9 ce 9 (L.) A column or pillar. 

Con'dyle 9 (Gr. novdvlog, Jcondulos, a knuckle, a protuberance.) A 
prominence on the end of a bone. 

Con-junc-ti'va, (L. can, together, and jungare, to join.) The mem- 
brane that covers the anterior part of the globe of the eye. 

Con-trac-tiV i-ty 9 (L. con, and trahere, to draw together.) The 
property of a muscle which enables it to contract, or draw its ex- 
tremities closer together. 

Con-vo-lu'tions 9 (L. con and where, to roll together.) The tortu- 
ous foldings of the external surface of the brain. 

Cor'ne-a 9 (L. cor'nu, a horn.) The transparent membrane which 
covers the anterior fifth of the eyeball. 

Cor f pns-cles 9 Blood, (L. dim. of cor* pus, a body.) The small bicon- 
cave disks which give to the blood its red color ; the white corpus- 
cles are globular and larger. 

Cos'ta 9 (L. costa, a coast, side, or rib.) A rib. 

Cra!ni-al 9 (L. cra'nium, the skull.) Pertaining to the skulL As 
the cranial nerves. 

Cvi'coid 9 (Gr. npinoc, krikos, a ring.) A cartilage of the larynx, re- 
sembling in shape a seal ring. 

Crystal-line Lens 9 (L. crystal' turn, a crystal.) One of the 
humors of the eye ; a double convex body situated in the front 
part of the eyeball. 

Cu'ti-cle 9 (L. dim. of cu'tis, the skin. The scarf-skin ; also called the 
epider'mis. 

Cu'tis 9 (Gr. okvtoc, skutos, the skin or hide.) The true skin, lying 
beneath the cuticle ; also called the der'ma. 

De-cus-sa' tion 9 (L. decus'sis, the Roman numeral ten, X.) A re- 
ciprocal crossing of fibres from side to side. 

Di'a-phragm 9 (Gr. Sia^puyfia, diaphragma, a partition.) The 



GLOSSARY. 360 

midriff; a muscle separating the cavity of the chest from the 
abdomen. 

Di-(t$ f to-lc, (Gr. diaaTeMeiv, diastelhin, to put asunder.) The dila- 
tation of the heart and arteries when the blood enters them. 

Dor'sal, (L. dorsum, the back.) Pertaining to the back. 

JDll-O-de'num, (L. duodc'ni, twelve.) The first division of the 
small intestines. 

Du'ra Ma'ter, (L. durus, hard, and mater, mother.) The outer- 
most membrane of the brain. 

E-mul'sion, (L. emulgere, to milk.) Oil in a finely divided state 
suspended in water. 

En-am' el, (Fr. email) The smooth hard material which covers the 
crown or visible part of the tooth. 

Ep-i-(jlot tis, (Gr. e-i, epi, upon, and ylurra, glotla, the tongue.) 
One of the cartilages of the glottis. 

East a ehi-an Tube. A channel from the fauces to the middle 
ear, named from Eustachius, who first described it. 

Ex-pi-ra'tion, (L. exspira're, to breathe out.) The act of forcing 
air out of the lungs. ' 

Ex-ten' sion, (L. ex, out, and tendere, to stretch.) The act of re- 
storing a limb, etc., to its natural position after it has been flexed, 
or bent ; the opposite of Flexion. 

Fas ci-a, (L. fascia, a band.) A tendinous expansion or aponeurosis. 

Fe-nes'tra, (L.) Literally, a window; the opening between the 
middle and internal ear. 

Fibrin. A peculiar organic substance found in animals and vege- 
tables ; it is solid, tough, elastic, and composed of thready fibers. 

Flex' ion, (L. fleeter?, to bend.) The act of bending. 

Fib'u-la, (L. a clasp.) The outer and lesser bone of the leg. 

Fol'li-ele, (L. foil i cuius, a small bag.) A gland ; a little bag in ani- 
mal bodies. 

Gan'f/li-on, (Gr. yayybiov, ganglion, a knot.) A knot-like swelling 
in the course of a nerve ; a smaller nerve-center. 

Gas' trie, (Gr. yaaTijp, gaster, stomach.) Pertaining to the stomach. 

Gland, (L. glans, an acorn.) An organ consisting of follicles and 
ducts, with numerous blood-vessels interwoven ; it separates some 
particular fluid from the blood. 

Glos'so-jtJtffr-f/n-f/e'al Nerve, (Gr. yluaaa, glossa, the tongue, 
and odfwi^ pharu nx, the throat.) The nerve of taste supplying 
the posterior third of the tongue ; it also supplies the throat. 

GlotftlSf (Gr.) The narrow opening at the upper part of the larynx. 

Qu&tO-tO-ry Nerve* The nerve of taste supplying the front 
part of the tongue ; a branch of the " fifth" pair. 

Hem'or-rhage, (Gr. unw, hoi' ma, blood, and fir'/yvv/ii, regnumi, to 
burst.) Bleeding, or the loss of blood. 



370 GLOSSARY. 

He-pat' ic, (Gr. faap, hepar, the liver.) Pertaining to the liver. 
Hy'gi-ene, (Gr. vyieta, huygieia, health.) The art of preserving 

health and preventing disease. 
In-cis'or, (L. incidere, to cut.) Applied to the four front teeth of 

both jaws, which have sharp cutting edges. 
ll'e-iim, (Gr. eiletv, eilein, to wind.) A portion of the small intes- 
tines. 
In-sal-i-va'tion, (L. in, and sali'va, the fluid of the mouth.) The 

mingling of the saliva with the food during the act of chewing. 
In-spi-ra'tion, (L. in, and spird're, to breathe.) The act of draw- 
ing in the breath. 
In-teg' u-ment, (L. in, and teg ere, to cover.) The skin, or outer 

covering of the body. 
I'ris, (L. i'ris, the rainbow.) The thin muscular ring which lies 

between the cornea and crystalline lens, and which gives the eye 

its brown, blue, or other color. 
In-ter-cost'al, (L. inter, between, and costa, a rib.) Between the 

ribs. 
Je-ju'num, (L. empty.) A portion of the small intestine. 
Ju'gu-lar, (L. jugulum, the neck.) Relating to the throat. The 

great veins of the neck. 
Lab'y-riuth, (Gr.) The internal ear, so named from its many 

windings. 
Lach'ry-mal 9 (L. lachryma, a tear.) Pertaining to tears. 
Lac'te-al, (L. lac, milk.) A small vessel or tube of animal bodies 

for conveying chyle from the intestine to tha thoracic duct. 
Lar'ynoc, (Gr.) The cartilaginous tube situated at the top of the 

windpipe, or trachea ; the organ of the voice. 
Lens, (L.) Literally, a lentil ; any transparent substance so shaped 

as either to converge or disperse the rays of light. 
Lig'a-ment, (L. ligare, to bind.) A strong fibrous material binding 

bones or other solid parts together. 
Ly))i2>h, (L- lympha, spring-water.) The colorless, watery fluid con- 
veyed by the lymphatic vessels. 
Mar'roiv, (Sax.) The soft, fatty substance contained in the central 

cavities of the bones. (The spinal marrow, however, is composed 

of nervous tissue.) 
]&as-ti-cd 'tion, (L. mastica're, to chew.) The act of cutting and 

grinding the food to pieces by means of the teeth. 
Me-dul'la Ob-lon-ga f ta. The " oblong marrow," or nervous cord, 

which is continuous with the spinal cord within the skull. 
Mem-hra'na Tym'pan-i, (L.) Literally, the membrane of the 

drum ; a delicate partition separating the outer from the middle ear. 
JMem'brane* A thin layer of tissue serving to cover some part of 

the body. 






GLOSSARY. 371 

Mi'tral, (L. mitre, a mitre.) The name of the valves in the left 

side of The heart. 
M.O r lar 9 (L. mold, a mill.) The name of some of the large teeth. 
Jlo'tor, (L. mocerc, to move.) Causing motion; the name of those 

nerves which conduct to the muscles the stimulus which causes 

them to contract. 
3fu' COIIS M())}'hr«)i(\ The thin layer of tissue which covers those 

internal cavities or passages which communicate with the external 

air. 
JIu'chs. A viscid fluid secreted by the mucous membrane, which it 

serves to moisten and defend. 
Na'sal, (L. nafsus, the nose.) Pertaining to the nose ; the nasal cavi- 
ties contain the distribution of the special nerve of smell. 
Nerve, (Gr. vevpov, neuron, a cord or string.) A glistening, white 

cord of cylindrical shape, connecting the brain or spinal cord with 

some other organ of the body. 
Nil-tri'tion, (L, nutrlre, to nourish.) The processes by which the 

nourishment of the body is accomplished. 
Oc'ci-put, (L. ob and caput, the head.) The hinder part of. the 

head. 
CE-soph' a-fjiis 9 (Gr.) Literally, that which carries food. The tube 

leading from the throat to the stomach. 
Ol-fac'fo-ry, (L. olfacere, to smell.) Pertaining to the sense of 

smell. 
Op'tic, (Gr. d-TLKog, from the root u-, future vipo/uai, opsomai, to see.) 

Pertaining to the sense of sight. 
Or'bit, (L. or'bis, the socket.) The bony socket or cavity in which 

the eyeball is situated. 
Os'tnose, (Gr. gjt/xoc, osmos, a thrusting or impulsion.) The process 

by which liquids are impelled through a moist membrane. 
Os'se-otfs. (L. OS, a hone.) Consisting of, or resembling bone. 
¥<il'(tt<\ (I.. pala'tum, the palate.) The roof of the mouth, consist- 
ing of the hard and soft palate. 
Pal' mar. Relating to the palm of the hand. 
Pan'cre-OS, (Gr. irdf, pas, all, and repeat, kreas, flesh.) A long, flat 

gland situated near the stomach. 
Pa-pll'la, <<' (L.) Small conical prominences. 
l*«-r<'ii'cli y-ma . (Gr. irape] \-i, parengchein, to pour through.) 

The substance contained between the blood-vessels of an organ. 
Pa-TOtfid, (Gr. napa 9 para $ near, and uror, otos, the ear.) The name 

of the larirfsT salivary gland. 

Pa-tel'la, (L. dim. of pafina, a paii.) Tin- knee-pan; a small 

bono. 
Pel' vis, (L.) Literally, a basin; the bony cavity at the lower part 

of the trunk. 



372 GLOSSARY. 

JPep'shi, (Gr. weirreLP, peptin, to digest.) The proximate organic 
element of the gastric juice. 

Per-i-car'di-um, (Gr. nepi, peri, around, and Kapdia, kardia, the 
heart.) A membrane that incloses the heart. 

I*er-i-cr<i r ni-um 9 (Gr. Kept, and Kpaviov,kr anion, the cranium.) A 
membrane that invests the skull. 

JPer-i-to-ue' 'inn, (Gr. nepiTelveiv, periteincin, to stretch around.) 
The investing membrane of the stomach, intestines, and other ab- 
dominal organs. 

Per-sjri-ra'tion, (L. perspirdre, to breathe through.) The sweat, 
or watery exhalation of the skin ; when visible, it is called sensible 
perspiration, when invisible, it is called insensible perspiration. 

JPhar'yn:r, (Gr. (jxipvyZ, pharunx, the throat.) The cavity between 
the back of the mouth and oesophagus. 

Phys-i-ol'o-r/ 1/ , (Gr. (pvatc, phuxis, nature, and "Xoyoc, logos, a dis- 
course.) The science of the functions of living, organized 
beings. 

J*Va Ma'ter, (L.) Literally, the tender mother ; the innermost of 
the three coverings of the brain. 

Pleu'ra, ce 9 (Gr. nXevpa, pleura, the side.) A thin membrane that 
covers the inside of the thorax, and also forms the exterior coat 
of the lungs. 

Pneu-ino-f/as'trlc, (Gr. kvev/liuv, pneumon, the lungs, and yaart/p, 
gaster, the stomach.) The name of a nerve distributed to the 
lungs and stomach ; it is the principal nerve of respiration. 

Prod 'ess, (L. procedure, to proceed, to go forth.) Any projection 
from a surface. Also, a method of performance ; a procedure. 

Pty'a-lhi, (Gr. nrvalov, plualon, saliva.) The peculiar organic in- 
gredient of the saliva. 

'EuU mo-na-ry 9 (L. puVmo, pulmo'nis, the lungs.) Pertaining to 
the lungs. 

T*y-lo'rtis, (Gr. izvhopoc, puloros, a gate-keeper.) The lower open- 
ing of the stomach, at the beginning of the small intestine. 

ttes-pi-raJ 'Hon, (L. re, again, and spirdre, to breathe.) The act of 
breathing. Inspiring air into the lungs and expelling it again. 

llet'i-na, (L. re'te, a net,) The innermost of the tunics or coats of 
the eyeball, being an expansion of the optic nerve. 

Sa'crum (L. sacred.) The bone which forms the posterior part of 
the pelvis, and is a continuation of the spinal column. 

Sa-U'va, (L.) The fluid which is secreted by the salivary glands. 

Scle-rot'ic, (Gr. gkItjpoc, skleros, hard.) The tough, fibrous outer 
tunic of the eyeball. 

Se-cre'tion, (L. secer r no, secre'tum, to separate.) The process of 
separating from the blood some essential important fluid ; which 
fluid is also called a secretion. 



GLOSSARY. 373 

Sefrum, (L.) The watery constituent of tlie blood, which separates 
from the clot daring the process of coagulation. 

Stti'prs. L. > Literally, a stirrup: one of the small bones of the 
tympanum, or middle ear, resembling somewhat a stirrup in shape 

Skel'e-ton, Gr wc . : o dry. The aggregate of the hard 

parts of the body : the boo - 

Sub-fin' f/ital, (L. sub, under, and lingua, the tongue.) Situated 
under the tongue. 

Sub-)}ia.i'U-!a-ri/, (L. sub. under, and maxilla, the jaw-bone.) Lo- 
cated under the jaw. 

Syn-o-vi-d. (Gr. n i . sm :. . resembling an egg.) The lubri- 

cating fluid of joints, so called because it resembles the white of egg. 

$!/$'to-le, (Gr. mariXXo, nuUilo, to contract.) The contraction of 
the heart, by which the blood is expelled from that orsrau. 

Tac'tile* L. tic'tus, touch.) Relating to the sense of touch. 

Ten'don, Gr. - m . r inmn, to stretch.) A hard, insensible cord, 
or bundle of fibers, by which a muscle is attached to a bone. 

T/io'ra.v. {Gr. - x, a breastplate.) The upper cavity of 

the trunk of the body, containing the lungs, heart, etc. : the chest. 

Hi //' void, Gr. (h i -;. tkureos, a shield.) The largest of the car- 
tilages of the larynx ; its angular projection in the front of the 
neck is called "Adam's apple." 

Tra'c7ie-a 9 (Gr. rpogvcj tra<;hus, rough.) The windpipe. 

Tym'pa-iium. (Gr. rvu-arov, tumpanon, a drum.) The cavity of 
the middle ear, resembling a drum in being closed by two mem- 
branes, and in having communication with the atmosphere. 

U'vu-la, (L. u>:a, a grape. i The small pendulous body attached to 
the back part of the palate. 

Yasfcu-lar* L. cas'culum. a little vessel.) Pertaining to, or con- 
taining blood- vessels. 

Ye' nous* [L. >:t'/ia,a vein.) Pertaining to, or contained within a vein. 

Yer'te-bral Column, (I* a, a joint.) The back-bone, con- 

sisting of twenty- four separate bones, called vertebrce, firmly jointed 
together ; also called the spinal column and spine. 

7', > ti-bule. A portion of the internal ear. communicating with the 
semicircular canals and the cochlea : so called from its fancied re- 
semblance to the vestibule or porch of a house. 

Villi, L the nap of cloth ) Minute thread-like projections 

found upon the internal surface of the small intestine, giving it a 
velvety appearance 

Yif re-otis. L. jlass.) Having the appearance of gl 

a] .plied to the humor occupying the largest part of the cavity of 
the eyeball. 

Vii'-ist ■<■' tint) . L. m» t alive, and .wire, to cut.) The practice of 
operating apon living animals, for the purpose of studying physi- 
ological processes. 



INDEX. 



PAGE 

Aberration., spherical 238 

chromatic 239 

Absorption 2 

by lacteals 98 

Aeration of the Blood, how clone.. . 144 
Agassiz, his doctrine of the multiple 

origin of the human race 312 

Air, composition of and changes in 
it by respiration 145 

agency of plants in keeping it pure 143 

Air-cells of the lungs 128 

Air-sacs in birds 144 

Alcoholic Stimulants, their influ- 
ence on health 209 

Alimentary Canal 90 

of different lengths in different 

animals 99 

Aneurism lv)G 

Animals, distinctions between them 
and plants 10 

intelligence of. 303 

Aorta, valves of 118 

Arm, bones of 43 

Arteries 106 

how to stop their bleeding 109 

Articulation of the voice 217 

Arytenoid Cartilages 211 

Bathing, how it should be practiced. 202 

Baya's nest 295 

Beaver, habits of. 301 

Birds, respiration of 14 1 

spinal column of 40 

Blood, its changes 114 

its course 115 

variety of textures made from it . . 159 

cells in it 108 

Bones, composition of IT 

uses of 17 

insensibility of. 21 

very sensible when inflamed 21 

Brain 180 

how guarded from violence 185 

its situation and connections 275 

hygiene of. 267 

Calisthenics 266 

Capillaries 

their agency in keeping up the cir- 
culation Ill 

Carnivorous Animals 83 

Carbonic Acid Gas, thrown oft* from 

the lungs 147 

where formed 143 

quantity of it discharged from the 

lungs 147 

absorbed by plants 148 



PAGE 

Carpus 19 

Cartilage 18 

Cells, the true formative vessels ... 168 

their shape 167 

their contents 107 

their selecting power 167 

two kinds in the blood 103 

cells perform absorption i;o 

and secretion in 

fibres of muscles made up of cells. 171 

cells make teeth, nails, &c 173 

how they make nerves 173 

all living things built by cells 173 

operation of cells in the egg dur- 
ing incubation .'. 174 

Cementum 32 

Cerebellum, functions of 203 

Chemical laws controlled by vital. . . 328 

Chin, possessed only by man 16 

Choroid coat of the eye 233 

Chyle 91 

Chyme 91 

Ciliary processes 234 

Circulation, its apparatus 105 

double 115 

Climate, influence of in causing the 

varieties of the race 316 

Coffee, influence of on health 270 

Cold, depressing influence of 201 

sometimes a stimulant 201 

Cold-blooded animals 153 

Collar bone 43 

Convolutions of the brain 200 

Cranium, bones of 27 

Cricoid Cartilage 212 

Crystalline lens 236 

Cuticle 162 

Death 335 

Deformity, how produced 316 

Deglutition 87 

Dentine 32 

Diaphragm 132 

Digestion 81 

hygiene of 251 

Disease, summary of its causes 271 

prevention of. 272 

Domestication, influence of 319 

Drowning explained 140 

Ear 220 

Egg, section of 224 

Elementary substances in animals 

and vegetables 13 

Enamel, structure of 32 

Epiglottis 211 

Erect posture of man 16 






INDEX. 



Ethiopian variety of the race 311 

Excretion, by what organs per- 
formed 161 

Exercise, influence of on digest* 

on the circulation 105 

Expiration, mode of performing. .. 132 

Expression effected by muscles 74 

Eye. optical instrument 229 

its defences 24(> 

Face, muscles of. ... 57 

Facial angle 883 

Far-sightedness 240 

Fingers, arrangements of tendons in 45 

Fishes, respiration of. 141 

spinal column in 40 

Food, quantity needed 251 

Foot, bones of -47 

Foruyce. his experiments on heat. . 15} 
Formation and repair, by what done 155 
Formative vessels, selecting power 

of 15S 

their concert of action illustrated 

in various ways 158 

Frog, changes from the tadpole 

slate 157 

Frontal Binns 29 

Functions, distinctions between nu- 
tritive and animal 12 

Ganglions 184 

Ric juice 89 

Gills, truly lungs 141 

Gizzard, in birds 102 

Gray substance of brain 904 

amount of compared with the white 

substance 282 

•ndence of mind on 285 

Gymnastics 206 

15 

Head, bones of 25, 27 

Heart, a forcing and suction pump. 106 

double 115 

valve- in 115 

it- a ventricles 116 

front view of IS 1 

map of 122 

tion of 128 

1 24 

tc 125 

125 

Heat of the body, how maintained. 1 1'» 

where marie . . 140 

I the fuel for it 150 

Its uniformity in man 152 

Herbivorous animals 

HlBBRNATK 156 

of it as a 

structure 

of 

Hydra 1 1 

11 

Hygiene, how it- principles are 



II v«»in bone 211 



PACE 

Iltim iiJ 

Inspiration, modeof performing. 1-3: 
Instinct more mysterious than rea- 
son 301 

uniformity of its action 301 

its perfection 

exhibited in communities of ani- 
mals 301 

blindness of it 302 

Involuntary muscles \. bl 

Iris 3.35 

Jaw, lower 31 

its digastric muscle (12 

Joints, lining of 49 

Knowledge, communicated only by 
muscles 74 

Lacte vls 98 

Larynx 211 

Lever, the three kinds of exempli- 
fied in the muscles 52 

Life, its origin and processes 320 

its nature unknown 327 

differs from other forces 327 

controls chemical forces 328 

sometimes dormant 330 

Light, refraction of. 230 

Lobworm, respiration of 141 

Locomotion, distinguishing animals 

from plants 10 

Lu-ngs, structure of 129 

Lymphatic absorbents 98 

Man, distinctions between him and 

animals 13 

Mastication 81 

Mechanical disadvantage under 

which muscles act ". 54 

Mesentery, plan of. 98 

Metacarpus 45 

Metatarsus 46 

Mind, influence of on digestion 253 

HfoNRODDo's notion 293 

Motion, involuntary 81 

Muscles 49 

their structure 19 

mods of action 51 

of arm 51 

of face and neck 57 

of the eye 64 

combined motions 65 

all knowledge communicated by.. 74 

their associated action 79 

\ w:.-. made by eells 172 

3IGHTBDNE8S 240 

- made from cells 173 

terminations of 181 

different sets of for different pur- 
poses 206 

- of the eye 

Of tli' 

Nervous system, di-tiiiL r ui>hinL r ani- 
iii.il— iiom regetablee . . 11 

its different pane 180 

. i im. membrane 940 



376 



INDEX. 



PAGE 

Nose, bones of. 31 

(Esophagus described 89 

Organic life, distinguished from 

animal life 12 

Organized and unorganized sub- 
stances 8 

difference between in permanency. 9 

in regularity . . 9 

OsTRfcH, respiratory apparatus of. . . 144 
Oxygen, absorbed by the lungs ex- 
haled by plants 148 

Patella 50 

action of the muscles on 60 

Pelvis 24 

Perspiration, influence of in ena- 
bling the body to bear very hot 

air 163 

Petrous (rock-like) bone 30 

Pharynx 88 

Plants, distinctions between them 

and animals 10 

Pleura. 129 

Plexuses of nerves 181 

Pylorus 92 

Radius 94 

Reaction against cold, how pro- 
duced 261 

Reason of a lower order in animals. 304 
Reasoning abstract, peculiar to man 309 

Reed instruments 215 

Respiration, its apparatus 127 

mechanism of 127 

hygiene of. 255 

Respiratory apparatus of fishes... 141 

of insects 143 

of birds 144 

Retina, structure of 234 

Ribs, arrangement of 131 

movement of in respiration 131 

Sacrum 36 

Salivary glands 85 

Scapula 43 

Sebaceous glands 163 

Semicircular canals 227 

Sensation, distinguishes animals 

from plants 10 

Skeleton, description of 22, 23 

Skin, structure and functions of 162 

hygiene of. 257 

Sound, how produced and trans- 
mitted 220, 222 

difference in transmission through 
solids, liquids and gases 222 

musical, how it differs from noise. 220 

how in the vocal instrument. . 213 



PAGE 

Species, how it differs from variety. 310 

Spinal column 36 

ofbirds 40 

of fishes and reptiles 41 

deformity of, how caused 264 

Spinal cord or marrow 18i 

its functions 181 

Stereoscope 242 

Stomach, uses in two senses 9 

distinguishing animals from 

plants 10 

its three coats 91 

difference of this organ in different 

animals 96 

Sutures of the skull 27 

Sweat glands 161 

Sympathetic system of nerves 206 

Tarsus 23 

Tailor-bird's nest 296 

Tea, influence of on health 270 

Tear-apparatus 247 

Teeth, different kinds 3.2 

structure of 32 

nerves in 32 

why second set needed 33 

Tendons 51 

Temporal bone 25 

Thigh bone 46 

Thoracic duet 8} 

Thyroid cartilage 21 1 

Tobacco, its influence on health 270 

Toggle-joint, exemplified in the 

joints of the body 71 

Tongue, its variety of motion 65 

Ulna 43 

Valves of the heart 120 

Veins, structure and situation of. . . . 107 

Ventilation, effects of, defective. . . 254 

Vertebrae described 35 

Visual angle 243 

Vitreous table of the bones of the 

skull 27 

Vocal ligaments 213 

Voice 206 

Waste of the system, by what or- 
gans thrown off 161 

influence of its retention 257 

Wasp's nest 298 

Water-scorpion, respiration of 143 

Whale, arrangement for catching 

its food 84 

its reservoirs for containing arte- 
rial blood 140 

Whispering, how done 219 

White substance of the brain 184 




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